Radiopaque cationically polymerizable compositions comprising a radiopacifying filler, and method for polymerizing same

ABSTRACT

Polymerizable compositions that include: (a) a cationically active functional group; (b) an initiation system capable of initiating cationic polymerization of the cationically active functional group; and (c) a filler composition that includes various radiopacifying fillers in an amount sufficient to render the polymerizable composition radiopaque. Components (a), (b), and (c) are selected such that the polymerizable composition polymerizes to form a polymerized composition having a Barcol hardness, measured using a GYZJ-935 meter, of at least 10 within 30 minutes following initiation of the cationically active functional group at a reaction temperature of 25° C.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.10/269,131, filed Oct. 11, 2002, now U.S. Pat. No. 7,030,049 which is adivision of U.S. patent application Ser. No. 09/898,219, filed Jul. 3,2001, now U.S. Pat. No. 6,465,541, which is a division of U.S. patentapplication Ser. No. 09/168,051, filed Oct. 7, 1998, now U.S. Pat. No.6,306,926.

BACKGROUND OF THE INVENTION

The invention relates to polymerizing radiopaque compositions thatinclude cationically active functional groups and radiopacifyingfillers.

Fillers are often added to polymer resins to form composites havinghigher strength values than the polymer resin itself. Dental composites,for example, typically feature high filler loadings on the order of 50%by weight or higher.

Non-radiopacifying fillers such as quartz and silica have beensuccessfully combined with free radically polymerizable components suchas acrylates and methacrylates and a free radical initiator to form auseful dental composite following exposure to polymerization conditions.Such fillers also have been successfully used with cationicallypolymerizable components such as epoxy resins and a cationic initiatorto form useful dental composites following cationic-initiatedpolymerization.

In many instances it is desirable to use a radiopacifying filler tocreate a radiopaque composite. Such composites are particularly usefulin dental applications because the composite is x-ray detectable.Radiopacifying fillers have been successfully combined with freeradically polymerizable components and free radical initiators to formdental composites. It would also be desirable to combine radiopacifyingfillers with cationic initiators and cationically polymerizablecomponents such as epoxy resins which undergo less shrinkage thanacrylates and methacrylates upon polymerization.

SUMMARY OF THE INVENTION

Although there is a need for a radiopaque composite prepared bycombining a cationic initiator, a cationically polymerizable componentand a radiopacifying filler, the inventors have discovered that, unlikefree radically polymerizable systems, not all polymerizableresin-filler-initiator combinations will produce a useful composite(i.e., a radiopaque composite having a Barcol hardness of at least 10measured using a GYZJ-935 meter) upon exposure to polymerizationconditions. In many cases, the inventors have discovered, theradiopacifying filler inhibits or suppresses the cationic polymerizationmechanism. In some cases, the net result is a composite having ahardness value lower than the hardness value of the unfilled resin.

The inventors have now discovered that certain radiopacifying fillers,when combined with cationic initiators and cationically polymerizablecomponents, will produce composites having a Barcol hardness of at least10 (measured using the GYZJ-935 meter) following exposure topolymerization conditions. In some cases, this requires treating fillersthat would otherwise interfere with the cationic polymerizationmechanism, e.g., by heating or coating the fillers. The inventors havefurther identified selection criteria that can be used to screencationic initiator-resin-radiopacifying filler combinations. Theinventors have thus made it possible to prepare useful composites basedupon cationic initiators, cationically polymerizable resins, andradiopacifying fillers.

Accordingly, the invention features, in a first aspect, a polymerizablecomposition that includes:

(a) a cationically active functional group;

(b) an initiation system capable of initiating cationic polymerizationof the cationically active functional group; and

(c) a filler composition comprising a radiopacifying filler in an amountsufficient to render the polymerizable composition radiopaque. Theradiopacifying filler is selected from the group consisting of metaloxides, metal halides, metal borates, metal phosphates, metal silicates,metal carbonates, metal germanates, metal tetrafluoroborates, metalhexafluorophosphates, and combinations thereof. The combinations may bein the form of physical blends or chemical compounds.

Components (a), (b), and (c) are selected such that the polymerizablecomposition polymerizes to form a polymerized composition having aBarcol hardness, measured according to Test Procedure A, infra, using aGYZJ-935 meter, of at least 10 within 30 minutes following initiation ofthe cationically active functional group at a reaction temperature of25□C. Initiation can be determined using differential scanningcalorimetry, and is manifested as an increase in enthalpy.

As used herein, a “radiopaque composition” is a composition that has theability to diminish the path of x-rays to the same extent as an aluminumsample having the same thickness such that the density of an x-ray imageof the composition is less than the density of the x-ray image of thealuminum, determined according to Procedure 7.11 of InternationalStandard ISO4049; 1988(E), “Dentistry—Resin-Based Filling Materials.”

A “cationically active functional group” is a chemical moiety that isactivated in the presence of an initiator capable of initiating cationicpolymerization such that it is available for reaction with othercompounds bearing cationically active functional groups.

A “free radically active functional group” is a chemical moiety that isactivated in the presence of an initiator capable of initiating freeradical polymerization such that it is available for reaction with othercompounds bearing free radically active functional groups.

A “metal oxide” is a compound that contains only a metal and oxygen.

A “metal halide” is a compound that contains, at a minimum, a metal anda halogen (e.g., chlorine, bromine, iodine, or fluorine).

A “metal borate” is a compound that contains, at a minimum, a metal,boron, and oxygen.

A “metal phosphate” is a compound that contains, at a minimum, a metal,phosphorous, and oxygen.

A “metal silicate” is a compound that contains, at a minimum, a metal,silicon, and oxygen. Thus, for example, a metal aluminosilicatecontaining a metal, aluminum, silicon, and oxygen would be considered a“metal silicate” for the purposes of this invention.

A “metal carbonate” is a compound that contains, at a minimum, a metaland a CO₃ group.

A “metal germanate” is a compound that contains, at a minimum, a metal,germanium, and oxygen.

A “metal tetrafluoroborate” is a compound that contains only a metal anda BF₄ group.

A “metal hexafluorophosphate” is a compound that contains only a metaland a PF₆ group.

The composition may also include a free radically polymerizablecomponent such as an acrylic or methacrylic acid ester. Suchcompositions are often referred to as “hybrid” compositions. In a hybridcomposition, free radical polymerization of the free radically activefunctional groups assists in obtaining the requisite Barcol hardnessvalue of the composite. Nevertheless, even in hybrid compositions it iscationic polymerization of the cationically active functional group thatpreferably forms a polymerized composition having the requisite hardnessvalue under the polymerization conditions described above.

In some embodiments, the polymerizable composition polymerizes to form apolymerized composition have a Barcol hardness, measured using aGYZJ-934-1 meter according to Test Procedure A, infra, of at least 10within 30 minutes following initiation of the cationically active group.

The inventors have identified several screening tests for use indesigning successful polymerizable compositions. Preferably, these testsare used in combination with each other.

One test focuses on the radiopacifying fillers themselves and is basedupon isoelectric point measurements. The isoelectric point of anyparticular radiopacifying filler is independent of filler loading.However, the filler loading influences which values of isoelectric pointare required in order to result in a successful cationic polymerization.According to this test, therefore, the filler composition is selectedsuch that when the amount of the radiopacifying filler is at least 50%by weight of the polymerizable composition, the radiopacifying fillerhas an isoelectric point, measured according to Test Procedure B, infra,of no greater than 7.

Other tests focus on the interaction between the radiopacifying fillerand a test polymerizable composition that includes a cationicallypolymerizable component and a cationic initiator. According to one suchtest, the filler composition is selected such that when the amount ofthe filler composition is 70% by weight of the polymerizablecomposition, a test polymerizable composition defined in Test ProcedureC, infra, that includes the filler composition has an adsorption valueof no greater than 20 micromoles/g filler, as determined by surface areatitration according to Test Procedure C. When the amount of the fillercomposition is 50% by weight of the polymerizable composition, theadsorption value is no greater than 80 micromoles/g filler.

According to another test, the filler composition is selected such thatwhen the amount of the filler composition is 70% by weight of thepolymerizable composition, the filler composition causes a change inconductivity of a test solution of no greater than 60 mV, determinedaccording to Test Procedure D, infra. When the amount of the fillercomposition is 50% by weight of the polymerizable composition, thechange in conductivity is no greater than 125 mV.

The selection criteria are phrased in terms of certain filler loadings.However, it should be understood that the particular filler loading isprovided as a test. Accordingly, polymerizable compositions havingfiller loadings different from the loadings associated with theselection criteria are within the scope of the invention provided that,for any particular filler/resin/initiator combination, if the fillerloading were the same as the amount recited in the selection criteria,the requirements of those criteria would be met.

Both the chemical composition and physical form of the radiopacifyingfiller, including its surface characteristics, as well as the processused to prepared the filler, are variables which influence the effect ofthe filler on the cationic polymerization mechanism for a givenpolymerizable resin-filler-initiator combination. Sol-gel-derived,melt-derived, vapor-derived, and mineral radiopacifying fillers can beused. The radiopacifying filler may also be in the form of one or moreinorganic radiopacifying particles dispersed in a polymer matrix. In thecase of sol-gel-derived fillers, the filler composition is selected suchthat the filler composition has a relative peak height of greater than80% as determined by Fourier transform infrared spectroscopy accordingto Test Procedure E, infra.

Semi-crystalline and amorphous microstructures are generally preferred.An “amorphous” filler is one which does not give rise to a discerniblex-ray powder diffraction pattern. A “semi-crystalline” filler is onewhich gives rise to a discernible x-ray powder diffraction pattern.

With respect to chemical composition, the radiopacifying fillerpreferably includes an element having an atomic number of at least 30.Examples include yttrium, strontium, barium, zirconium, hafnium,niobium, tantalum, tungsten, molybdenum, tin, zinc, lanthanide elements(i.e., elements having atomic numbers ranging from 57 to 71, inclusive),and combinations thereof. Particularly preferred are radiopacifyingfillers that include: (a) an oxide selected from the group consisting oflanthanum oxide, zinc oxide, tantalum oxide, tin oxide, zirconium oxide,yttrium oxide, ytterbium oxide, barium oxide, strontium oxide, andcombinations thereof, combined with (b) an oxide selected from the groupconsisting of aluminum oxide, boron oxide, silicon oxide, andcombinations thereof. Specific examples of suitable radiopacifyingfillers include the following:

(a) Fillers that include 0.5% to 55% by weight lanthanum oxide and 45%to 99% by weight silicon oxide. The fillers preferably have asemi-crystalline or amorphous microstructure. In terms of processing,the fillers are preferably sol-gel- or melt-derived.

(b) Fillers that include 0.5% to 55% by weight lanthanum oxide, 0.5% to50% by weight aluminum oxide, and 0.5% to 90% by weight silicon oxide.The fillers preferably have a semi-crystalline or amorphousmicrostructure. In terms of processing, the fillers ar preferablysol-gel- or melt-derived.

(c) Fillers that include 0.5% to 55% by weight lanthanum oxide, 0.1% to55% by weight aluminum oxide, 0.01% to 80% by weight boron oxide, and 1%to 90% by weight silicon oxide. The fillers preferably have an amorphousmicrostructure. In terms of processing, the fillers are preferablysol-gel- or melt-derived.

(d) Fillers that include 0.5% to 55% by weight lanthanum oxide, 0.01% to80% by weight boron oxide, and 1% to 90% by weight silicon oxide. Thefillers preferably have a semi-crystalline or amorphous microstructure.In terms of processing, the fillers are preferably sol-gel- ormelt-derived.

(e) Fillers that include 0.5% to 55% by weight zinc oxide, 0.5% to 55%by weight lanthanum oxide, 0.1% to 40% by weight aluminum oxide, 0.01%to 80% by weight boron oxide, and 1% to 80% by weight silicon oxide. Thefillers preferably have an amorphous microstructure. In terms ofprocessing, the fillers are preferably melt-derived.

(f) Fillers that include colloidally derived zirconium oxide.

(g) Fillers that include 0.5% to 55% by weight zirconium oxide and 45%to 99% by weight silicon oxide. The fillers preferably have asemi-crystalline or amorphous microstructure. In terms of processing,the fillers are preferably sol-gel-derived.

(h) Fillers that include 0.5% to 55% by weight zirconium oxide, 0.01% to40% by weight boron oxide, and 1% to 90% by weight silicon oxide. Thefillers preferably have a semi-crystalline or amorphous microstructure.In terms of processing, the fillers are preferably sol-gel-derived.

(i) Fillers that include 0.5% to 55% by weight yttrium oxide and 1% to90% by weight silicon oxide. The fillers preferably have asemi-crystalline or amorphous microstructure. In terms of processing,the fillers are preferably derived from a sol-gel. The fillerspreferably have a semi-crystalline or amorphous microstructure. In termsof processing, the fillers are preferably sol-gel-derived.

(j) Fillers that include 0.5% to 55% by weight yttrium oxide, 0.1% to50% by weight aluminum oxide, and 1% to 90% by weight silicon oxide. Thefillers preferably have a semi-crystalline or amorphous microstructure.In terms of processing, the fillers are preferably sol-gel- ormelt-derived.

(k) Fillers that include 0.5% to 55% by weight barium oxide, 0.1% to 40%by weight aluminum oxide, 0.01% to 80% by weight boron oxide, and 1% to90% silicon oxide. The filler preferably has an amorphousmicrostructure. In terms of processing, the fillers are preferably ismelt-derived.

(l) Fillers that include 0.5% to 55% by weight strontium oxide, 0.1% to40% by weight aluminum oxide, 0.01% to 80% by weight boron oxide, and 1%to 90% by weight silicon oxide. The filler preferably has an amorphousmicrostructure. In terms of processing, the fillers are preferablyderived from a melt.

(m) Fillers that include a fluoride such as a lanthanide fluoride (e.g.,ytterbium fluoride), yttrium fluoride, zinc fluoride, tin fluoride, andcombinations thereof.

In some cases, the above-described radiopacifying fillers may be used“as is.” In other cases, it is necessary to treat the fillers, e.g., byheat treating the fillers or by coating them. Accordingly, even fillerswhich do not meet the above-described selection criteria initially canbe used successfully if treated properly.

The coated radiopacifying fillers include a core having a first chemicalcomposition and a coating (which may or may not be continuous) on thesurface of the core having a second chemical composition different fromthe first chemical composition. Examples of useful core materialsinclude quartz, fused quartz, silicate glass (including borosilicateglass), zirconium oxide-silicon oxide, zirconium oxide-boronoxide-silicon oxide, and combinations thereof. Examples of usefulcoatings include silicate glass (including borosilicate glass), boronoxide, colloidally derived silicon oxide, colloidally derived zirconiumoxide, and combinations thereof. Polymer coatings can also be used. Insome cases, the coating offers the additional advantages of reducingshrinkage upon polymerization and opacity. The reduced opacity, in turn,enhances the ability to obtain good depth of cure in photopolymerizablecompositions. The coating may also provide anchorage for, e.g., silanetreatments.

The amount of filler composition preferably is at least 50% by weight,and more preferably at least 70% by weight, based upon the total weightof the polymerizable composition. In addition to the radiopacifyingfiller, the filler may include non-radiopacifying fillers such asquartz, calcium carbonate, feldspar, KBF₄, cryolite, and combinationsthereof.

The initiator system is preferably a photoinitiator system.Photoinitiated compositions preferably polymerize to form a polymerizedcomposition having a depth of cure of at least 2 mm, preferably at least6 mm, and more preferably at least 8 mm within 30 minutes followinginitiation of the cationically active functional group at a reactiontemperature of 37° C. Useful initiator systems include onium salts suchas iodonium and sulfonium salts, and organometallic complex salts.

Examples of suitable materials having cationically active functionalgroups include epoxy resins, vinyl ethers, spiro ortho esters, spiroortho carbonates, bicylic ortho esters, bicyclic monolactones, bicyclicbislactones, cyclic carbonates, and combinations thereof. Such materialscan be used alone or combined with reactants having free radicallyactive functional groups to form hybrid compositions. It is alsopossible to include reactants that contain both free radically activefunctional groups and cationically active functional groups in a singlemolecule.

In the case of hybrid compositions, the composition may include aseparate initiator system capable of initiating free radicalpolymerization of the free radically active functional group.Alternatively, the composition may include a single initiator systemcapable of initiating both free radical and cationic polymerization.

Examples of useful polymerizable compositions include dental composites,orthodontic bracket adhesives, and orthodontic band cements. As usedherein, the term “composite” refers to a filled dental material. Theterm “restorative” refers to a composite which is polymerized after itis disposed adjacent to a tooth. The term “prosthesis” refers to acomposite which is polymerized for its final use (e.g., as crown,bridge, veneer, inlay, onlay or the like) before it is disposed adjacentto a tooth. The term “sealant” refers to a lightly filled compositewhich is polymerized after it is disposed adjacent to a tooth. Each ofthese materials is suitable for temporary or permanent use.

In a second aspect, the invention features a photopolymerizable dentalcomposite that includes:

(a) a cationically active functional group;

(b) a photoinitiation system capable of initiating cationicpolymerization of the cationically active functional group upon exposureto visible light; and

(c) a filler composition comprising a radiopacifying filler in an amountsufficient to render the polymerizable composition radiopaque. Uponexposure to visible light, the composite polymerizes to form apolymerized dental composite having a Barcol hardness, measuredaccording to Test Procedure A, infra, using a GYZJ-935 meter, of atleast 10 within 30 minutes following initiation of the cationicallyactive functional group at a reaction temperature of 25° C. Thecomposite may further include an ethylenically unsaturated reactant, asdescribed above.

Preferably, the resulting composite has a Barcol hardness, measuredusing a GYZJ-934-1 meter according to Test Procedure A, of at least 10within 30 minutes following initiation of the cationically activefunctional group at a reaction temperature of 25° C. The amount offiller in the composite preferably is at least 50% by weight based uponthe total weight of the polymerizable composite. The compositepreferably polymerizes to form a polymerized composite having a depth ofcure of at least 2 mm within 30 minutes following initiation of thecationically active functional group at a reaction temperature of 37° C.

In a third aspect, the invention features a polymerizable compositionthat includes:

(a) a cationically active functional group;

(b) an initiation system capable of initiating cationic polymerizationof the cationically active functional group; and

(c) a filler composition comprising a radiopacifying filler other than asulfate in an amount sufficient to render the polymerizable compositionradiopaque. Components (a), (b), and (c) are selected such that thepolymerizable composition polymerizes to form a polymerized compositionhaving a Barcol hardness, measured according to Test Procedure A, infra,using a GYZJ-935 meter, of at least 10 within 30 minutes followinginitiation of the cationically active functional group at a reactiontemperature of 25° C.

In a fourth aspect, the invention features a method of preparing apolymerized composition that includes:

(a) providing a polymerizable composition that includes (i) acationically active functional group; (ii) an initiation system capableof initiating cationic polymerization of the cationically activefunctional group; and (iii) a filler composition that includes aradiopacifying filler in an amount sufficient to render the compositionradiopaque; and

(b) initiating polymerization of said cationically active functionalgroup to form said polymerized composition, preferably at a reactiontemperature of 37° C. or less. The radiopacifying filler is selectedfrom the group consisting of metal oxides, metal halides, metal borates,metal phosphates, metal silicates, metal carbonates, metal germanates,metal tetrafluoroborates, metal hexafluorophosphates, and combinationsthereof, where these terms have the meanings set forth above. Thepolymerizable composition is selected such that it is capable ofpolymerizing to form a polymerized composition having a Barcol hardness,measured according to Test Procedure A, infra, using a GYZJ-935 meter,of at least 10 within 30 minutes following initiation of thecationically active functional group at a reaction temperature of 25° C.Examples of useful polymerized products include dental composites.

In one embodiment, the initiation system is a photoinitiation system, inwhich case the method includes exposing the polymerizable composition toactinic radiation to initiate polymerization of the cationically activefunctional group. Preferably, the initiation system includes a visiblelight sensitizer as well such that polymerization is initiated byexposing the composition to visible light. Other suitable sources ofactinic radiation include sources of ultraviolet radiation. Thermalinitiation systems may also be used, in which case the method includesexposing the composition to thermal radiation to initiate polymerizationof the cationically active functional group.

The inventors have further discovered a number of novel fillers. Suchfillers are useful in both free radically polymerizable compositions,cationically polymerizable compositions, and hybrid compositionsfeaturing both free radically and cationically polymerizable components.Some of these fillers have high clarity and form composites havingrelatively low opacity with respect to visible light. Some of thesefillers also exhibit low surface area and low residual porosity.

One filler is a melt-derived filler that includes 5–25% by weightaluminum oxide, 10–35% by weight boron oxide, 15–50% by weight lanthanumoxide, and 20–50% by weight silicon oxide.

Another filler is a melt-derived filler that includes 10–30% by weightaluminum oxide, 10–40% by weight boron oxide, 20–50% by weight siliconoxide, and 15–40% by weight tantalum oxide.

A third filler is a melt-derived filler that includes 5–30% by weightaluminum oxide, 5–40% by weight boron oxide, 0–15% by weight lanthanumoxide, 25–55% by weight silicon oxide, and 10–40% by weight zinc oxide.

A fourth filler is a melt-derived filler that includes 15–30% by weightaluminum oxide, 15–30% by weight boron oxide, 20–50% by weight siliconoxide, and 15–40% by weight ytterbium oxide.

A fifth filler is in the form of non vitreous microparticles prepared bya sol-gel method in which an aqueous or organic dispersion or sol ofamorphous silicon oxide is mixed with an aqueous or organic dispersion,sol, or solution of a radiopacifying metal oxide, or precursor organicor inorganic compound. The microparticles are substantially free ofcrystalline microregions or inhomogeneities detectable via powder x-raydiffraction.

A sixth filler is in the form of non vitreous microparticles prepared bya sol-gel method in which an aqueous or organic dispersion or sol ofamorphous silicon oxide is mixed with an aqueous or organic dispersion,sol, or solution of a radiopacifying metal oxide, or precursor organicor inorganic compound. The microparticles include: (i) a plurality ofamorphous microregions comprising oxygen and silicon, (ii) a pluralityof radiopacifying, semicrystalline, metal oxide microregions, and (iii)no greater than about 40% by weight of B₂O₃ or P₂O₅. The amorphousmicroregions are substantially uniformly interspersed with thesemicrystalline microregions. In addition, the microparticles aresubstantially free of crystalline microregions or inhomogeneities havingdiameters greater than 0.4 micrometers.

Other features and advantages of the invention will be apparent from thefollowing description of preferred embodiments thereof, and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) and 1(b) are plots of Barcol hardness (GYZJ-935 at 30minutes post-illumination) vs. isoelectric point, measured according toTest Procedure B, for composites having filler loadings of 50 and 70%(w/w/), respectively.

FIGS. 2( a) and 2(b) are plots of Barcol hardness (GYZJ-935 at 30minutes post-illumination) vs. adsorption values, measured according toTest Procedure C, for composites having filler loadings of 50 and 70%(w/w), respectively.

FIGS. 3( a) and 3(b) are plots of Barcol hardness (GYZJ-935 at 30minutes post-illumination) vs. conductivity change, measured accordingto Test Procedure D, for composites having filler loadings of 50 and 70%(w/w), respectively.

FIGS. 4( a) and 4(b) are plots of Barcol hardness (GYZJ-935 at 30minutes post-illumination) vs. percent peak height, measured accordingto Test Procedure E, for composites having filler loadings of 50 and 70%(w/w), respectively.

FIG. 5 is an adsorption isotherm analysis (Test Procedure C) featuring aplot of Barcol hardness (GYZJ-934-1) vs. photoinitiator concentration.

DETAILED DESCRIPTION

The invention provides filled, radiopaque, cationically polymerizablecompositions that undergo cationically initiated polymerization to formuseful composites. Free radically polymerizable reactants and initiatorsmay be included as well. The compositions are particularly suitable fordental applications. The inventors have discovered that by carefullyselecting the individual components of the composition, including theinitiator, polymerizable components, and radiopacifying filler, theproblem of the filler inhibiting or suppressing cationic polymerization,and thereby preventing formation of a suitably hard composite, can beavoided. The selection process involves using the screening testsidentified in the Summary of the Invention, above, to design appropriatefiller-polymerizable resin-initiator combinations. For best results, thetests should be used in conjunction with each other.

The individual components of the polymerizable composition will now bedescribed.

Filler Composition

The filler composition preferably forms at least 50% by weight, and morepreferably at least 70% by weight, of the polymerizable composition.Lower filler loadings, however, may be used as well. It includes atleast one radiopacifying filler. The amount of radiopacifying filler issufficient to render the polymerizable composition radiopaque. Suitableradiopacifying fillers are described in the Summary of the Invention,above. Preferably, the fillers have a semi-crystalline or amorphousmicrostructure.

Commercially available sources of radiopacifying fillers are describedin the Examples, infra. Alternatively, the radiopacifying fillers may besynthesized using ceramic processing techniques including sol-gelprocessing, melt processing, vapor phase processing, and colloidalprocessing.

In some instances, a particular radiopacifying filler that does notsatisfy the above-identified screening tests can be treated such thatthe resulting filler composition then passes one or more of these tests.The treatment modifies the surface characteristics of the filler andthus its interaction with the other components of the polymerizablecomposition. For example, heat-treating the filler can convert aseemingly unusable radiopacifying filler into a useful filler. Theparticular heat-treatment temperature is a function of the individualfiller. In general, however, heat-treatment temperatures for bothmelt-derived and sol-gel-derived fillers are on the order of about 400°C. or higher.

Another treatment protocol involves coating the filler particles withone or more materials having a composition different from that of thecore filler. Examples of suitable coatings include low temperaturemelting amorphous materials applied in the form of sols (e.g., colloidalsols such as colloidal zirconium oxide sols) and then optionally fired,polymers, and polymerizable monomers. Suitable coating techniquesinclude spray drying, magnetic coating, tray drying, vapor coating,flame spraying, electrostatic spraying, fluidized bed processes, andsol-gel processes.

Other examples of useful treatment protocols which can be used to alterthe surface characteristics of the radiopacifying filler include wetmilling (in the case of glass fillers), grinding, and the incorporationof fluxing agents such as boron oxide during filler preparation.

The filler composition may also include non-radiopacifying fillers.Examples include quartz, fused quartz, fumed silica, calcium carbonate,feldspar, KBF₄, cryolite, and combinations thereof.

Initiation System

One class of useful initiators includes sources of species capable ofinitiating both free radical and cationic polymerization. Representativeexamples include onium salts and mixed ligand arene cyclopentadienylmetal salts with complex metal halide ions, as described in “CRCHandbook of Organic Photochemistry”, vol II, ed. J. C. Scaiano, pp.335–339 (1989). Preferably, the source is an onium salt such as asulfonium or iodonium salt. Of the onium salts, iodonium salts (e.g.,aryl iodonium salts) are particularly useful. The iodonium salt shouldbe soluble in the composition and preferably is shelf-stable, meaning itdoes not spontaneously promote polymerization when dissolved therein inthe presence of the cationic polymerization modifier and photosensitizer(if included). Accordingly, selection of a particular iodonium salt maydepend to some extent upon the particular polymerizable reactants,cationic polymerization modifiers, and sensitizers (if present).

Suitable iodonium salts are described in U.S. Pat. Nos. 3,729,313;3,741,769; 4,250,053; and 4,394,403, the iodonium salt disclosures ofwhich are incorporated herein by reference. The iodonium salt can be asimple salt, containing an anion such as Cl⁻, Br⁻, I⁻, C₄H₅SO₃ ⁻, orC(SO₂CF₃)₃ ⁻; or a metal complex salt containing an antimonate,arsenate, phosphate, or borate such as SbF₅OH⁻, AsF₆ ⁻, or B(C₆F₅)₄ ⁻.Mixtures of iodonium salts can be used if desired.

Examples of useful aromatic iodonium complex salt photoinitiatorsinclude: diphenyliodonium tetrafluoroborate; di(4-methylphenyl)iodoniumtetrafluoroborate; phenyl-4-methylphenyliodonium tetrafluoroborate;di(4-heptylphenyl)iodonium tetrafluoroborate; di(3-nitrophenyl)iodoniumhexafluorophosphate; di(4-chlorophenyl)iodonium hexafluorophosphate;di(naphthyl)iodonium tetrafluoroborate;di(4-trifluoromethylphenyl)iodonium tetrafluoroborate; diphenyliodoniumhexafluorophosphate; di(4-methylphenyl)iodonium hexafluorophosphate;diphenyliodonium hexafluoroarsenate; di(4-phenoxyphenyl)iodoniumtetrafluoroborate; phenyl-2-thienyliodonium hexafluorophosphate;3,5-dimethylpyrazolyl-4-phenyliodonium hexafluorophosphate;diphenyliodonium hexafluoroantimonate; 2,2′-diphenyliodoniumtetrafluoroborate; di(2,4-dichlorophenyl)iodonium hexafluorophosphate;di(4-bromophenyl)iodonium hexafluorophosphate;di(4-methoxyphenyl)iodonium hexafluorophosphate;di(3-carboxyphenyl)iodonium hexafluorophosphate;di(3-methoxycarbonylphenyl)iodonium hexafluorophosphate;di(3-methoxysulfonylphenyl)iodonium hexafluorophosphate;di(4-acetamidophenyl)iodonium hexafluorophosphate;di(2-benzothienyl)iodonium hexafluorophosphate; diphenyliodoniumhexafluoroantimonate; diphenyl or diaryliodoniumtristrifluoromethylsulfonyl methide; or diphenyl or diaryliodoniumtetra(pentafluorophenyl)borate.

The initiation system may also include a sensitizer such as a visiblelight sensitizer that is soluble in the polymerizable composition. Thesensitizer preferably is capable of absorbing light having wavelengthsin the range from about 300 to about 1000 nanometers.

Examples of suitable sensitizers include ketones, coumarin dyes (e.g.,ketocoumarins), xanthene dyes, acridine dyes, thiazole dyes, thiazinedyes, oxazine dyes, azine dyes, aminoketone dyes, porphyrins, aromaticpolycyclic hydrocarbons, p-substituted aminostyryl ketone compounds,aminotriaryl methanes, merocyanines, squarylium dyes, and pyridiniumdyes. Ketones (e.g., monoketones or alpha-diketones), ketocoumarins,aminoarylketones, and p-substituted aminostyryl ketone compounds arepreferred sensitizers. For applications requiring deep cure (e.g., cureof highly filled composites), it is preferred to employ sensitizershaving an extinction coefficient below about 100 lmole⁻ ¹cm⁻¹, morepreferably about or below 100 lmole⁻ cm⁻¹, at the desired wavelength ofirradiation for photopolymerization. The alpha-diketones are an exampleof a class of sensitizers having this property, and are particularlypreferred for dental applications.

Examples of particularly preferred visible light sensitizers includecamphorquinone; glyoxal; biacetyl; 3,3,6,6-tetramethylcyclohexanedione;3,3,7,7-tetramethyl-1.2-cycloheptanedione;3,3,8,8-tetramethyl-1,2-cyclooctanedione;3,3,18,18-tetramethyl-1,2-cyclooctadecanedione; dipivaloyl; benzil;furil; hydroxybenzil; 2,3-butanedione; 2,3-pentanedione;2,3-hexanedione; 3,4-hexanedione; 2,3-heptanedione; 3,4-heptanedione;2,3-octanedione; 4,5-octanedione; and 1,2-cyclohexanedione; Of these,camphorquinone is the most preferred sensitizer.

In some cases it may be desirable to delay the onset of cationicpolymerization. For example, in the case of a hybrid composition thatincludes both free radically active functional groups and cationicallyactive functional groups, it may be desirable to use an initiationsystem suitable for initiating both free radical and cationicpolymerization which is designed such that for a given reactiontemperature, photoinitiation of free radical polymerization occurs aftera finite induction period T₁ and photoinitiation of cationicpolymerization occurs after a finite induction period T₃, where T₃ isgreater than T₁. T₁ and T₃ are measured relative to administration ofthe first dose of actinic radiation which occurs at T₀. Such initiationsystems are described in Oxman et al., “Compositions FeaturingCationically Active and Free Radically Active Functional Groups, andMethods for Polymerizing Such Compositions,” U.S. Pat. No. 6,187,836,which is assigned to the same assignee as the present application andhereby incorporated by reference. As described therein, thephotoinitiation system includes: (i) a source of species capable ofinitiating free radical polymerization of the free radically activefunctional group and cationic polymerization of the cationically activefunctional group; and (ii) a cationic polymerization modifier. Theamount and type of modifier are selected such that in the absence of themodifier, initiation of cationic polymerization under the sameirradiation conditions occurs at the end of a finite induction period T₂(also measured relative to T₀), where T₂ is less than T₃.

The induction periods (T₁, T₂, and T₃) can be measured usingdifferential scanning calorimetry. Following the first irradiation eventat T₀, the enthalpy of the reaction is measured as a function of time.Both initiation of free radical polymerization and initiation ofcationic polymerization result in an increase in enthalpy, observed as apair of separate peaks on the graph. The time at which initiation occursis taken to be the time at which the enthalpy begins to rise.

The cationic polymerization modifier preferably has a photoinducedpotential less than that of 3-dimethylaminobenzoic acid in a standardsolution of 2.9×10⁻⁵ moles/g diphenyliodonium hexafluoroantimonate and1.5×10⁻⁵ moles/g camphorquinone in 2-butanone, measured according to theprocedure described in the aforementioned Oxman et al. application. Ingeneral, useful cationic polymerization modifiers are typically baseshaving pK_(b) values, measured in aqueous solution, of less than 10.Examples of classes of suitable cationic polymerization modifiersinclude aromatic amines, aliphatic amines, aliphatic amides, aliphaticureas; aliphatic and aromatic phosphines, and salts of organic orinorganic acids (e.g., salts of sulfinic acid). Specific examplesinclude 4-(dimethylamino)phenylacetic acid, dimethylaminophenethanol,dihydroxy p-toluidine, N-(3,5-dimethylphenyl)-N,N-diethanolamine,2,4,6-pentamethylaniline, dimethylbenzylamine, N,N-dimethylacetamide,tetramethylurea, N-methyldiethanolamine, triethylamine,2-(methylamino)ethanol, dibutylamine, diethanolamine, N-ethylmorpholine,trimethyl-1,3-propanediamine, 3-quinuclidinol, triphenylphosphine,sodium toluene sulfinate, tricyclohexylphosphine, N-methylpyrollidone,and t-butyldimethylaniline. These modifiers may be used alone or incombination with each other, or with a material having photoinducedpotential greater than that of 3-dimethylaminobenzoic acid in a standardsolution of 2.9×10⁻⁵ moles/g diphenyliodonium hexafluoroantimonate and1.5×10⁻⁵ moles/g camphorquinone in 2-butanone; an example of such amaterial is ethyl 4-(dimethylamino)benzoate (“EDMAB”).

In other cases, it may be desirable to accelerate initiation of cationicpolymerization. For example, in certain hybrid compositions it may bedesirable to achieve near-simultaneous initiation of the free radicallyactive functional groups and the cationically active functional groups.Examples of suitable initiation systems for accomplishing this objectiveare described in Oxman et al. entitled “Ternary Photoinitiator Systemfor Curing of Epoxy/Polyol Resin Compositions,” U.S. Pat. No. 6,025,406,and Oxman et al., entitled “Ternary Photoinitiator System for Curing ofEpoxy Resins,” U.S. Pat. No. 5,998,495, both of which are assigned tothe same assignee as the present application and hereby incorporated byreference. As described therein, the photoinitiator system includes aniodonium salt (e.g., an aryliodonium salt), a visible light sensitizer(e.g., camphorquinone), and an electron donor. The systems have aphotoinduced potential greater than or equal to that of3-dimethylaminobenzoic acid in a standard solution of 2.9×10⁻⁵ moles/gdiphenyliodonium hexafluoroantimonate and 1.5×10⁻⁵ moles/gcamphorquinone in 2-butanone, measured according to the proceduredescribed in the aforementioned Oxman et al. applications. An example ofa suitable electron donor is ethyl 4-(dimethylamino)benzoate (“EDMAB”).

In the case of hybrid compositions that include both free radicallyactive functional groups and cationically active functional groups, itmay be desirable to use one initiation system for free radicalpolymerization and a separate initiation system for cationicpolymerization. The free radical polymerization initiation system isselected such that upon activation, only free radical polymerization isinitiated.

One class of initiators capable of initiating polymerization of freeradically active functional groups, but not cationically activefunctional groups, includes conventional chemical initiator systems suchas a combination of a peroxide and an amine. These initiators, whichrely upon a thermal redox reaction, are often referred to as “auto-curecatalysts.” They are typically supplied as two-part systems in which thereactants are stored apart from each other and then combined immediatelyprior to use.

A second class of initiators capable of initiating polymerization offree radically active functional groups, but not cationically activefunctional groups, includes free radical-generating photoinitiators,optionally combined with a photosensitizer or accelerator. Suchinitiators typically are capable of generating free radicals foraddition polymerization at some wavelength between 200 and 800 nm.Examples include alpha-diketones, monoketals of alpha-diketones orketoaldehydes, acyloins and their corresponding ethers,chromophore-substituted halomethyl-s-triazines, andchromophore-substituted halomethyl-oxadiazoles.

A third class of initiators capable of initiating polymerization of freeradically active functional groups, but not cationically activefunctional groups, includes free radical-generating thermal initiators.Examples include peroxides and azo compounds such as AIBN.

The dual initiation systems further include a separate photoinitiationsystem for initiating polymerization of the cationically activefunctional groups. The cationic initiation system is selected such thatactivation of the free radical initiation system does not activate thecationic initiation system. Examples of suitable cationicphotoinitiation systems for a dual initiation system composition includethe onium salts and mixed ligand arene cyclopentadienyl metal salts withcomplex metal halide ions described above.

Polymerizable Compounds

The polymerizable compositions include cationically active functionalgroups and, optionally, free radically active functional groups.Materials having cationically active functional groups includecationically polymerizable epoxy resins. Such materials are organiccompounds having an oxirane ring, i.e., a group of the formula

which is polymerizable by ring opening. These materials includemonomeric epoxy compounds and epoxides of the polymeric type and can bealiphatic, cycloaliphatic, aromatic or heterocyclic. These materialsgenerally have, on the average, at least 1 polymerizable epoxy group permolecule, preferably at least about 1.5 and more preferably at leastabout 2 polymerizable epoxy groups per molecule. The polymeric epoxidesinclude linear polymers having terminal epoxy groups (e.g., a diglycidylether of a polyoxyalkylene glycol), polymers having skeletal oxiraneunits (e.g., polybutadiene polyepoxide), and polymers having pendentepoxy groups (e.g., a glycidyl methacrylate polymer or copolymer). Theepoxides may be pure compounds or may be mixtures of compoundscontaining one, two, or more epoxy groups per molecule. The “average”number of epoxy groups per molecule is determined by dividing the totalnumber of epoxy groups in the epoxy-containing material by the totalnumber of epoxy-containing molecules present.

These epoxy-containing materials may vary from low molecular weightmonomeric materials to high molecular weight polymers and may varygreatly in the nature of their backbone and substituent groups.Illustrative of permissible substituent groups include halogens, estergroups, ethers, sulfonate groups, siloxane groups, nitro groups,phosphate groups, and the like. The molecular weight of theepoxy-containing materials may vary from about 58 to about 100,000 ormore.

Useful epoxy-containing materials include those which containcyclohexane oxide groups such as epoxycyclohexanecarboxylates, typifiedby 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. For amore detailed list of useful epoxides of this nature, reference is madeto the U.S. Pat. No. 3,117,099, which is incorporated herein byreference.

Further epoxy-containing materials which are useful in the compositionsof this invention include glycidyl ether monomers of the formula

where R′ is alkyl or aryl and n is an integer of 1 to 6. Examples areglycidyl ethers of polyhydric phenols obtained by reacting a polyhydricphenol with an excess of chlorohydrin such as epichlorohydrin (e.g., thediglycidyl ether of 2,2-bis-(2,3-epoxypropoxyphenol)-propane). Furtherexamples of epoxides of this type are described in U.S. Pat. No.3,018,262, which is incorporated herein by reference, and in “Handbookof Epoxy Resins” by Lee and Neville, McGraw-Hill Book Co., New York(1967).

There are a host of commercially available epoxy resins which can beused in this invention. In particular, epoxides which are readilyavailable include octadecylene oxide, epichlorohydrin, styrene oxide,vinylcyclohexene oxide, glycidol, glycidyl methacrylate, diglycidylether of Bisphenol A (e.g., those available under the trade designations“Epon 828”, “Epon 825”, “Epon 1004” and “Epon 1010” from Shell ChemicalCo., “DER-331”, “DER-332”, and “DER-334”, from Dow Chemical Co.),vinylcyclohexene dioxide (e.g., “ERL-4206” from Union Carbide Corp.),3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexene carboxylate (e.g.,“ERL-4221” or “CYRACURE UVR 6110” or “UVR 6105” from Union CarbideCorp.),3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methyl-cyclohexenecarboxylate (e.g., “ERL-4201” from Union Carbide Corp.),bis(3,4-epoxy-6-methylcyclohexylmethyl)adipate (e.g., “ERL-4289” fromUnion Carbide Corp.), bis(2,3-epoxycyclopentyl)ether (e.g., “ERL-0400”from Union Carbide Corp.), aliphatic epoxy modified from polypropyleneglycol (e.g., “ERL-4050” and “ERL-4052” from Union Carbide Corp.),dipentene dioxide (e.g., “ERL-4269” from Union Carbide Corp.),epoxidized polybutadiene (e.g., “Oxiron 2001” from FMC Corp.), siliconeresin containing epoxy functionality, flame retardant epoxy resins(e.g., “DER-580”, a brominated bisphenol type epoxy resin available fromDow Chemical Co.), 1,4-butanediol diglycidyl ether of phenolformaldehydenovolak (e.g., “DEN-431” and “DEN-438” from Dow Chemical Co.), andresorcinol diglycidyl ether (e.g., “Kopoxite” from Koppers Company,Inc.), bis(3,4-epoxycyclohexyl)adipate (e.g., “ERL-4299” or “UVR-6128”,from Union Carbide Corp.),2-(3,4-epoxycyclohexyl-5,5-spiro-3,4-epoxy)cyclohexane-meta-dioxane(e.g., “ERL-4234” from Union Carbide Corp.), vinylcyclohexene monoxide1,2-epoxyhexadecane (e.g., “UVR-6216” from Union Carbide Corp.), alkylglycidyl ethers such as alkyl C₈–C₁₀ glycidyl ether (e.g., “HELOXYModifier 7” from Shell Chemical Co.), alkyl C₁₂–C₁₄ glycidyl ether(e.g., “HELOXY Modifier 8” from Shell Chemical Co.), butyl glycidylether (e.g., HELOXY Modifier 61” from Shell Chemical Co.), cresylglycidyl ether (e.g., “HELOXY Modifier 62” from Shell Chemical Co.),p-ter butylphenyl glycidyl ether (e.g., “HELOXY Modifier 65” from ShellChemical Co.), polyfunctional glycidyl ethers such as diglycidyl etherof 1,4-butanediol (e.g., “HELOXY Modifier 67” from Shell Chemical Co.),diglycidyl ether of neopentyl glycol (e.g., “HELOXY Modifier 68” fromShell Chemical Co.), diglycidyl ether of cyclohexanedimethanol (e.g.,“HELOXY Modifier 107” from Shell Chemical Co.), trimethylol ethanetriglycidyl ether (e.g., “HELOXY Modifier 44” from Shell Chemical Co.),trimethylol propane triglycidyl ether (e.g., “HELOXY Modifier 48” fromShell Chemical Co.), polyglycidyl ether of an aliphatic polyol (e.g.,“HELOXY Modifier 84” from Shell Chemical Co.), polyglycol diepoxide(e.g., “HELOXY Modifier 32” from Shell Chemical Co.), bisphenol Fepoxides (e.g., “EPN-1138” or “GY-281” from Ciba-Geigy Corp.),9,9-bis[4-(2,3-epoxypropoxy)phenyl]fluorenone (e.g., “Epon 1079” fromShell Chemical Co.).

Still other epoxy resins contain copolymers of acrylic acid esters orglycidol such as glycidylacrylate and glycidylmethacrylate with one ormore copolymerizable vinyl compounds. Examples of such copolymers are1:1 styrene-glycidylmethacrylate, 1:1methylmethacrylate-glycidylacrylate and a 62.5:24:13.5methylmethacrylate-ethyl acrylate-glycidylmethacrylate.

Other useful epoxy resins are well known and contain such epoxides asepichlorohydrins, alkylene oxides, e.g., propylene oxide, styrene oxide;alkenyl oxides, e.g., butadiene oxide; glycidyl esters, e.g., ethylglycidate.

Blends of various epoxy-containing materials are also contemplated.Examples of such blends include two or more weight average molecularweight distributions of epoxy-containing compounds, such as lowmolecular weight (below 200), intermediate molecular weight (about 200to 10,000) and higher molecular weight (above about 10,000).Alternatively or additionally, the epoxy resin may contain a blend ofepoxy-containing materials having different chemical natures, such asaliphatic and aromatic, or functionalities, such as polar and non-polar.

Other types of useful materials having cationically active functionalgroups include vinyl ethers, oxetanes, spiro-orthocarbonates,spiro-orthoesters, and the like.

Materials having free radically active functional groups includemonomers, oligomers, and polymers having one or more ethylenicallyunsaturated groups. Suitable materials contain at least oneethylenically unsaturated bond, and are capable of undergoing additionpolymerization. Such free radically polymerizable materials includemono-, di- or poly-acrylates and methacrylates such as methyl acrylate,methyl methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexylacrylate, stearyl acrylate, allyl acrylate, glycerol diacrylate,glycerol triacrylate, ethyleneglycol diacrylate, diethyleneglycoldiacrylate, triethyleneglycol dimethacrylate, 1,3-propanedioldiacrylate, 1,3-propanediol dimethacrylate, trimethylolpropanetriacrylate, 1,2,4butanetriol trimethacrylate, 1,4-cyclohexanedioldiacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate,pentaerythritol tetramethacrylate, sorbitol hexacrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane, andtrishydroxyethyl-isocyanurate trimethacrylate; the bis-acrylates andbis-methacrylates of polyethylene glycols of molecular weight 200–500,copolymerizable mixtures of acrylated monomers such as those in U.S.Pat. No. 4,652,274, and acrylated oligomers such as those of U.S. Pat.No. 4,642,126; and vinyl compounds such as styrene, diallyl phthalate,divinyl succinate, divinyl adipate and divinylphthalate. Mixtures of twoor more of these free radically polymerizable materials can be used ifdesired.

If desired, both cationically active and free radically activefunctional groups may be contained in a single molecule. Such moleculesmay be obtained, for example, by reacting a di- or poly-epoxide with oneor more equivalents of an ethylenically unsaturated carboxylic acid. Anexample of such a material is the reaction product of UVR-6105(available from Union Carbide) with one equivalent of methacrylic acid.Commercially available materials having epoxy and free-radically activefunctionalities include the “Cyclomer” series, such as Cyclomer M-100,

M-101, or A-200 available from Daicel Chemical, Japan, and Ebecryl-3605available from Radcure Specialties.

Other Additives

The polymerizable composition may further include a hydroxy containingmaterial. Suitable hydroxyl-containing materials can be any organicmaterial having hydroxyl functionality of at least 1, and preferably atleast 2. Preferably, the hydroxyl-containing material contains two ormore primary or secondary aliphatic hydroxyl groups (i.e., the hydroxylgroup is bonded directly to a non-aromatic carbon atom). The hydroxylgroups can be terminally situated, or they can be pendent from a polymeror copolymer. The molecular weight of the hydroxyl-containing organicmaterial can vary from very low (e.g., 32) to very high (e.g., onemillion or more). Suitable hydroxyl-containing materials can have lowmolecular weights, i.e. from about 32 to 200, intermediate molecularweight, i.e. from about 200 to 10,000, or high molecular weight, i.e.above about 10,000. As used herein, all molecular weights are weightaverage molecular weights.

The hydroxyl-containing materials can be non-aromatic in nature or cancontain aromatic functionality. The hydroxyl-containing material canoptionally contain heteroatoms in the backbone of the molecule, such asnitrogen, oxygen, sulfur, and the like. The hydroxyl-containing materialcan, for example, be selected from naturally occurring or syntheticallyprepared cellulosic materials. Of course, the hydroxyl-containingmaterial is also substantially free of groups which may be thermally orphotolytically unstable; that is, the material will not decompose orliberate volatile components at temperatures below about 100° C. or inthe presence of actinic light which may be encountered during thedesired polymerization conditions for the free radically activecomponents of the polymerizable composition.

Representative examples of suitable hydroxyl-containing materials havinga hydroxyl functionality of 1 include alkanols, monoalkyl ethers ofpolyoxyalkyleneglycols, monoalkyl ethers of alkylene-glycols, and othersknown in the art.

Representative examples of useful monomeric polyhydroxy organicmaterials include alkylene glycols (e.g., 1,2-ethanediol;1,3-propanediol; 1,4-butanediol; 1,6-hexanediol; 1,8-octanediol;2-ethyl-1,6-hexanediol; bis(hydroxymethyl)cyclohexane;1,18-dihydroxyoctadecane; 3-chloro-1,2-propanediol); polyhydroxyalkanes(e.g., glycerine, tri-methylolethane, pentaerythritol, sorbitol) andother polyhydroxy compounds; 2-butyne-1,4-diol;4,4-bis(hydroxymethyl)diphenylsulfone; castor oil; and the like.

Representative examples of useful polymeric hydroxyl-containingmaterials include polyoxyethylene and polyoxypropylene glycols, andparticularly the polyoxyethylene and polyoxypropylene glycol diols andtriols having molecular weights from about 200 to about 10,000corresponding to a hydroxy equivalent weight of 100 to 5000 for thediols or 70 to 3300 for triols; polytetramethylene ether glycols such aspolytetrahydrofuran or “poly THF” of varying molecular weight;copolymers of hydroxypropyl and hydroxyethyl acrylates and methacrylateswith other free radical-polymerizable monomers such as acrylate esters,vinyl halides, or styrene; copolymers containing pendent hydroxy groupsformed by hydrolysis or partial hydrolysis of vinyl acetate copolymers,polyvinylacetal resins containing pendent hydroxyl groups; modifiedcellulose polymers such as hydroxyethylated and hydroxypropylatedcellulose; hydroxy-terminated polyesters; hydroxy-terminatedpolylactones, and particularly the polycaprolactones; fluorinatedpolyoxyethylene or polyoxypropylene glycols; and hydroxy-terminatedpolyalkadienes.

Useful commercially available hydroxyl-containing materials include the“TERATHANE” series of polytetramethylene ether glycols such as“TERATHANE” 650, 1000, 2000 and 2900 (available from du Pont de Nemours,Wilmington, Del.) the “PEP” series of polyoxyalkylene tetrols havingsecondary hydroxyl groups such as “PEP” 450, 550 and 650; “BUTVAR”series of polyvinylacetal resins such as “BUTVAR” B-72A, B-73, B-76,B-90 and B-98 (available from Monsanto Chemical Company, St. Louis,Mo.); and the “FORMVAR” series of resins such as 7/70, 12/85, 7/95S,7/95E, 15/95S and 15/95E (available from Monsanto Chemical Company); the“TONE” series of polycaprolactone polyols such as “TONE” 0200, 0210,0230,0240, 0300 and 0301 (available from Union Carbide); “PARAPLEXU-148” aliphatic polyester diol (available from Rohm and Haas,Philadelphia, Pa.), the “MULTRON” R series of saturated polyesterpolyols such as “MULTRON” R-2, R-12A, R-16, R-18, R-38, R-68 and R-74(available from Mobay Chemical Co.); “KLUCEL E” hydroxypropylatedcellulose having an equivalent weight of approximately 100 (availablefrom Hercules Inc.); “Alcohol Soluble Butyrate” cellulose acetatebutyrate ester having a hydroxyl equivalent weight of approximately 400(available from Eastman Kodak Co., Rochester, N.Y.); polyether polyolssuch as polypropylene glycol diol (e.g., “ARCOL PPG-425”, “ArcolPPG-725”, “ARCOL PPG-1025”, “ARCOL PPG-2025”, ARCOL PPG-3025”, “ ARCOLPPG-4025” from ARCO Chemical Co.); polypropylene glycol triol (e.g.,“ARCOL LT-28”, “ARCOL LHT-42”, “ARCOL LHT 112”, “ARCOL LHT 240”, “ARCOLLG56”, “ARCOL LG-168”, “ARCOL LG-650” from ARCO Chemical Co.); ethyleneoxide capped polyoxypropylene triol or diol (e.g., “ARCOL 11–27”, “ARCOL11–34”, “ARCOL E-351”, “ARCOL E-452”, “ARCOL E-785”, “ARCOL E-786” fromARCO Chemical Co.); ethoxylated bis-phenol A; propylene oxide orethylene oxide—based polyols (e.g., “VORANOL” polyether polyols from theDow Chemical Co.).

The amount of hydroxyl-containing organic material used in thepolymerizable compositions may vary over broad ranges, depending uponfactors such as the compatibility of the hydroxyl-containing materialwith the epoxide and/or free radically polymerizable component, theequivalent weight and functionality of the hydroxyl-containing material,the physical properties desired in the final composition, the desiredspeed of polymerization, and the like.

Blends of various hydroxyl-containing materials may also be used.Examples of such blends include two or more molecular weightdistributions of hydroxyl-containing compounds, such as low molecularweight (below 200), intermediate molecular weight (about 200 to 10,000)and higher molecular weight (above about 10,000). Alternatively, oradditionally, the hydroxyl-containing material can contain a blend ofhydroxyl-containing materials having different chemical natures, such asaliphatic and aromatic, or functionalities, such as polar and non-polar.As an additional example, one may use mixtures of two or morepoly-functional hydroxy materials or one or more mono-functional hydroxymaterials with poly-functional hydroxy materials.

The polymerizable material(s) can also contain hydroxyl groups and freeradically active functional groups in a single molecule. Examples ofsuch materials include hydroxyalkylacrylates andhydroxyalkylmethacrylates such as hydroxyethylacrylate,hydroxyethylmethacrylate; glycerol mono- or di-(meth)acrylate;trimethylolpropane mono- or di-(meth)acrylate, pentaerythritol mono-,di-, and tri-(meth)acrylate, sorbitol mono-, di-, tri-, tetra-, orpenta-(meth)acrylate; and2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane.

The polymerizable material(s) can also contain hydroxyl groups andcationically active functional groups in a single molecule. An exampleis a single molecule that includes both hydroxyl groups and epoxygroups.

The polymerizable composition can also contain suitable additives suchas fluoride sources, anti-microbial agents, accelerators, stabilizers,absorbers, pigments, dyes, viscosity modifiers, surface tensiondepressants and wetting aids, antioxidants, and other ingredientswell-known to those skilled in the art. The amounts and types of eachingredient should be adjusted to provide the desired physical andhandling properties before and after polymerization.

Polymerization Procedure

The polymerizable compositions are preferably prepared by admixing,under “safe light” conditions, the various components of thecompositions. Suitable inert solvents may be employed if desired wheneffecting the mixture. Examples of suitable solvents include acetone,dichloromethane, and acetonitrile.

In the case of single initiation systems, polymerization is effected byexposing the composition to a radiation source, preferably a visiblelight source. It is convenient to employ light sources that emitultraviolet or visible light such as quartz halogen lamps,tungsten-halogen lamps, mercury arcs, carbon arcs, low-, medium-, andhigh-pressure mercury lamps, plasma arcs, light emitting diodes, andlasers.

In general, useful light sources have intensities in the range of200–500 mW/cm². One example, which is particularly useful for dentalapplications, is a Visilux dental curing light commercially availablefrom 3M Company of St. Paul, Minn. Such lights have an intensity ofabout 200 mW/cm² at a wavelength of 400–500 nm.

The exposure may be effected in several ways. For example, thepolymerizable composition may be continuously exposed to radiationthroughout the entire polymerization process. It is also possible toexpose the composition to a single dose of radiation, and then removethe radiation source, thereby allowing polymerization to occur. In thecase of hybrid compositions, the composition preferably is initiallyexposed to a single dose of radiation to initiate polymerization of thefree radically active functional groups, followed by exposure to asecond dose of radiation to initiate polymerization of the cationicallyactive functional groups.

The invention will now be described further by way of the followingexamples.

EXAMPLES Test Procedures

A. Hardness

The hardness of each composite following polymerization provides ameasure of whether or not any particular filled composition inhibits orsuppresses cationic polymerization. Two Barcol Hardness meters (modelsGYZJ-934-1 and GYZJ-935; Barber Coleman, Inc., Loves Park, Ill.) areused. These meters are monitored for performance consistency using a setof calibration disks provided with the meter.

Each prepolymerized composite is packed into a 5 mm diameter sphericalcutout in a 4 mm deep Delrin mold. Mylar film is used as a liner on eachside of the mold to ensure that the mold is filled completely, and thatthe sample is flush with the mold surface. The sample is then exposed toheat or actinic radiation to initiate polymerization.

Each sample is tested following polymerization using the two meters bypressing the tip of the tester firmly against the composite surface in asmooth, flat area of the sample. Two readings are taken at the topsurface immediately after removing the heat or radiation source, and at30 minutes, and the mean reading at each time point is reported. Bothhardness meters are used in order to rank cure, with the the BarcolGYZJ-935 discriminating medium hard plastics, and the GYZJ-934-1measuring hard plastics. All values registering less than 10 onGYZJ-934-1 are tested using GYZJ-935. Samples registering above 80 onthe GYZJ-935 meter are remade and retested on GYZJ-934-1 meter.

B. Isoelectric Point

The isoelectric point is measured using a Matec Electrokinetic SonicAnalysis System MBS-8000 (Matec Applied Sciences, Hopkinton, Mass.). Theprobe magnitude and polarity is calibrated with a 10% (v/v) Ludoxsolution. A 12 g sample of filler is dispersed into 228 g of distilledwater to give an approximately 5% (w/w) dispersion. The zeta potentialis measured while titrating over the pH range of 1 to 10 using 1.0 N HCland 1.0 N NaOH. The zeta potential is plotted as a function of the pH.The isoelectric point is reported as the pH at which the zeta potentialis equal to zero.

C. Adsorption Isotherm Analysis

Fillers are dried at 150° C. for 1 week and stored in a desiccator. Asurface area titration is performed by measuring the Barcol hardness(GYZJ-934-1 at 30 minutes post illumination) of a series of compositescontaining 70% (w/w) of a filler at photoinitiator concentrationsranging from 0.1% to 15% (w/w). In order to minimize refractive indexmismatch with concomitant reduced depth of cure, resin B2 (describedbelow) is chosen so that the refractive index of the resin blendapproximately match that of the filler tested. The Barcol hardness(GYZJ-934-1 at 30 minutes) is plotted against the initial photoinitiatorconcentration in the resin (undiluted by filler), as shown in FIG. 5 inthe case of a representative filler (filler (1), described below). Theamount of photoinitiator-derived species adsorbed or inactivated on thesurface of filler is calculated by determining the concentration ofinitiator required to achieve full cure (C). Since full cure in anunfilled resin systems is obtained at photoinitiator concentrations muchlower that those used in this test of filled resins, the simplifyingassumption is made that full cure is obtained even when vanishinglysmall concentrations of photoinitiator-derived species are present. Thiswas confirmed by experiment.

The photoinitiator concentration can be expressed as C=C_(o)–C_(f). WhenC_(f)=O, all initiator-derived species are adsorbed or inactivated,resulting in no cure of the resin. The maximum concentration ofinitiator-derived species adsorbed or otherwise inactivated by thefiller is then given by C=C_(o), as shown in FIG. 5.

The amount of the initiator-derived species that is adsorbed to thefiller surface or otherwise inhibited is related to the adsorbance (Γ),BET surface area of the filler (SA) and the weight of the filler in thecomposite (W) as follows:Initiator adsorbed or inhibited=(W) (SA)

  (1)

The amount of initiator in the resin (moles) is related to itsconcentration and the volume of the resin:Initiator change=(V) (C)   (2)

V=volume of unfilled resin (mL)

C=concentration of initiator in resin

C_(o)=initial concentration of initiator in resin

C_(f)=final concentration of initiator in resin

W=weight of solids

SA=specific area of solids (m²/g) determined by BET

=adsorbance of initiator derived species normalized to filler surfacearea(μmoles/m²)

=adsorbance of initiator derived species (μmoles/g filler)

The adsorbance of the photoinitiator-derived species

μmoles/g filler) or the adsorbance per unit surface area of filler

μmoles/m²) is calculated. In order to solve for the adsorbance, we notethat within the parameters of the material set, the presence of evenvanishingly small amounts of photoinitiator will cause complete cure inthe absence of filler in the time frame of the test. For example, in theabsence of filler, complete cure is obtained at concentrations of lessthan 0.1% (w/w) iodonium (CD 1012) whereas most screening tests utilize1–15% (w/w) iodonium. Therefore, for these tests, we can assume that thepresence of any uninhibited photoinitiator derived species would resultin substantial cure in the presence of filler at 30 minutes. Therefore,we can relate the inhibition of cure, as measured by Barcol hardness, tothe concentration of photoinitiator-derived species that are adsorbed ordeactivated by equating equations (1) and (2):initiator change=initiator derived species adsorbed or deactivated  (3a)(V) (C _(o))=(W) (SA)

  (3b)Rearranging, we can solve for the adsorbance

in equation   (4)

=(V) (C _(o))/(W) (SA)   (4)

The dependence on the BET surface area can be removed from theadsorbance by multiplying, as in equation (5), to give the absorbanceper gram of filler.

=

×SA   (5)D. Conductivity

Fillers are dried at 150° C. for 1 week and stored in a desiccator.Methyl ethyl ketone and anhydrous ethanol supplied by J. T. Baker(Phillipsburg, N.J.) are dried over molecular sieves. Exposure to humid,ambient conditions is avoided. A stock solution is prepared containing0.25 parts CPQ, 1.5 parts Sartomer CD1012, 0.5 partsethyl-4-dimethylaminobenzoate and 97.75 parts of a 90/10 weight/weightmethyl ethyl ketone/anhydrous ethanol solution. A sample of 4 grams ofstock solution is weighed into a glass vial. A calibrated glass pHelectrode (Corning PN 476540) is placed into the solution and a Beckman210 pH meter is zeroed on the solution. The pH meter is standardizedperiodically in pH4 and pH7 buffer solutions.

The vial is irradiated for 20 seconds with a 3M™ XL 3000™ dental curinglight. The initial solution conductivity is read in millivolts andrecorded as E₀. 1.0 g sample of filler is added to the 4 g of irradiatedstock solution and stirred vigorously for up to 45 seconds. Theconductivity is measured and allowed to come to equilibrium. The finalconductivity is measured and recorded as E. The conductivity change isexpressed as the difference between the initial and final conductivity.

After obtaining the final conductivity reading, the electrode is rinsedwith a dried mixture of 2-butanone and ethanol, gently wiped, andallowed to dry for 30–60 seconds prior to use on the next test.

E. FTIR Analysis

Fillers are dried at 150° C. for 1 week and stored in a desiccator.Samples are prepared as Nujol mulls. Four drops (approximately 0.08 ml)of ethyl acetate (Fluka Chemika 99.5% (GC)) are added to a 1cc portionof Nujol (mineral oil USP—Paddock Laboratories, Inc.). Approximately twodrops (approximately 0.04 ml) of the Nujol/ethyl acetate mixture isadded to approximately 300 mg of dried filler (150° C. for 1 week) andmulled to form a highly filled, cohesive mull. The sample is placedbetween NaCl plates for presentation to the FTIR. The NaCl plate issanded on one surface with 500 grit Wet-or-Dry sandpaper (3M Company) topresent a rough surface to facilitate spreading the mull and to preventinterference fringes seen when polished surfaces are used.

All spectra are recorded in the absorbance mode on the Bomem MB-102 FTIR(Bomem/Hartman & Braun, Quebec, Quebec Canada). Sixteen scans (at 4 cm⁻¹resolution) are co-added per spectrum. In the absence of filler, ethylacetate in Nujol shows an absorbance band at 1747 cm⁻¹ The relativeratio of peak height at 1747 cm⁻¹ to that of the total peak height dueto ethyl acetate in the presence of filler is calculated. For example,when the presence of filler causes a shift to 1703, 1710 and 1726 cm⁻¹,the relative peak height is calculated as follows:% P _(H,1747 cm−1)=(100*P _(H,1747))/[P _(H,1747) +P _(H,1703) +P_(H,1710) +P _(H,1726)].

A value % P_(H,1747 cm) ⁻¹ of 100% denotes no interaction of the fillersurface with ethyl acetate.

The measurement of peak height was done using a commercial program(Grams32 Galactic) which allows the use of preselected baseline points(from a “flat” area of the spectrum) and the selection of the height tobe measured.

F. Depth of Cure

Three composite pastes are prepared by combining 3 parts of resin with 7parts of filler. The pastes are filled into syringes, and de-bubbledunder pressure at 45° C. for 24 hours. The pastes are then extruded intocylindrical nylon molds (diameter≅6 mm) with heights ranging from 2 to 8mm. The filled molds are warmed to 37° C. by placing them in an oven for30 minutes, after which time they are irradiated for 60 seconds with a3M model 5530 dental curing light. The irradiated samples are thenreturned to the 37° C. oven. Thirty minutes later the samples areremoved and tested for Barcol hardness (GYZJ-934-1) on the bottom of thesample, as described in Test Procedure A.

G. Karl Fisher Titration

The moisture content of fillers is measured using a 652KF Coulometer(Metrohm, Houston, Tex.). Samples are prepared in a dry box.Approximately 1 g of filler is weighed into a serum vial. A 10 mL sampleof methanol is added to the vial which is sealed with a serum cap andweighed. Samples are placed a shaker for 2–6 hours, after which time thefiller is allowed to settle by standing overnight. Three vials areprepared per filler sample for triplicate readings.

A sample of the supernatant is withdrawn from the vial using a 20 gaugeneedle and syringe. A 0.45 micron filter is then placed on the end of asyringe and the filtered sample injected into the Karl Fischer titrator.The sample is titrated iodometrically as described in QuantitativeChemical Analysis (Harris).

H. B.E.T. Surface Area

The surface area is determined using nitrogen adsorption in asingle-point Brunauer-Emmet-Tell (BET) method, as described by S. J.Gregg and K. S. W. Sing in Adsorption, Surface Area, and Porosity(Academic Press Inc., London 1982). Approximately 12 grams of sample isplaced into the chamber of the Horiba SA-6210 (Irvine, Calif.) samplepreparation station and degassed for 10–12 hours at 200 C. The surfacearea of the sample is measured on a Horiba SA-6201 twice, and both theoutgassed and repeated measurement are compared. The out gassedmeasurement is reported.

I. Particle Size

Particle size is measured using a Horiba LA-910 laser light scatteringinstrument. Particle size is measured in three media. The particle sizeof dry filler is measured using the Horiba dry powder attachment,Powderjet. The primary particle size of filler when dispersed in aqueoussolution is measured by dispersing 0.2–0.4% (w/w) filler into a bufferedaqueous solution containing Liquinox, Tween 80, Calgon, and NaF andapplying an ultrasonic horn and a magnetic stirrer for 10 minutes.Sufficient sample is added to a solution of surfactant solution in thetest chamber in order to give a transmittance of approximately 85%.Particle size is reported as the mean volume diameter (microns).

J. Refractive Index (n_(D))

The refractive index of the filler particles is measured using the BeckeLine Method, as described in Practical Refractometry by Means of aMicroscope (Roy M. Allen, 2^(nd) Edition, Cargille, N.J.).

K. Specific Gravity

Specific gravity (g/cc) is measured using a Micromeritics (Norcross,Ga.) AccuPyc 1330 helium pycnometer.

L. X-Ray Diffraction (XRD)

X-ray diffraction is performed with copper K-alpha radiation on either aPhillips vertical diffractometer or a Picker 4 circle diffractometer.“Am” means amorphous, “unid.ph.” means unidentified phase,“unid.crys.ph.” means unidentified crystalline phase, “T” meanstetragonal structure, “pc” means pseudo-cubic structure, “c” means cubicstructure, and “crist. unid.” means alpha-cristobalite and unidentifiedcrystalline phase.

M. Fluorescence

Fluorescent behavior of fillers is observed under illumination by aSpectroline ENF-260C long wavelength UV light (Spectronics Corp.,Westbury, N.Y.). Bright fluorescence is noted with a capital letter ofthe color observed; dull fluorescence is noted with a small letter(y=yellow, w=white, b=blue). No fluorescence is noted with the letter“N”.

N. Radiopacity

The radiopacity of polymerized samples is determined according to theprocedure specified in Section 7.11 of the International Standard ISO4049:1988 (E).

O. Diametrile Tensile Strength (DTS)

For DTS measurements the uncured composite samples were injected into3.2 mm inner diameter, 9.5 mm outer diameter rigid acrylic tubes. Thefilled tubes were subjected to 2.2–2.9 kg/cm² (30–40 psi) pressure for 5minutes, followed by curing while under pressure by exposure to twoVisilux-2 (3M, St. Paul) dental curing lights for 80 seconds. The curedsamples were allowed to stand for 5 minutes without applied pressure andthen were placed in 37° C. deionized water for 1–2 hours before cuttingto length. The samples were cut on a diamond saw to form cylindricalplugs approximately 1.5 mm long for measurement of diametrile tensilestrength. Five samples of each material were prepared for DTS results.The plugs were stored in deionized water at approximately 37° C. forabout 16–24 hours and their DTS values then determined according toAmerican Dental Association specification No. 27 using an InstronMechanical Testing Instrument (Model 1123).

P. Compressive Strength (CS)

For CS measurements the uncured composite samples were injected into 3.2mm inner diameter, 9.5 mm outer diameter rigid acrylic tubes. The filledtubes were subjected to 2.2–2.9 kg/cm² (30–40 psi) pressure for 5minutes, followed by curing while under pressure by exposure to twoVisilux-2 (3M, St. Paul) dental curing lights for 80 seconds. The curedsamples were allowed to stand for 5 minutes without applied pressure andthen were placed in 37° C. deionized water for 1–2 hours before cuttingto length. The samples were cut on a diamond saw to form cylindricalplugs approximately 6 mm long for measurement of compressive strength.Five samples of each material were prepared for CS results. The plugswere stored in deionized water at approximately 37° C. for about 16–24hours and their CS values then determined according to American DentalAssociation specification No. 27 using an Instron Mechanical TestingInstrument (Model 1123).

Q. Visual Opacity

Disc-shaped, one millimeter thick by 20 millimeter diameter samples ofthe composite were cured by exposing them to illumination from a 3MVisilux-2 dental curing light for 60 seconds on each side of the disk ata distance of 6 millimeters. The cured composite samples were thenevaluated for visual opacity by measuring transmission of light throughthe thickness of the disk using a MacBeth transmission densitometerModel TD-504 equipped with a visible light filter.

Composite Preparation

Six different polymerizable resin compositions were made by preparing aseries of stock solutions and then combining a given stock solution witha given initiator solution. The various stock solutions are describedbelow. All amounts are given in w/w percent. The stock solutions wereprepared by mixing the components using a Vertishear Cyclone I.Q. at 600rpm for 10 minutes on ice.

Stock Solutions

Component Stock A1 Stock A2 Stock A3 Stock A4 pTHF 20 20 20 15.5 UVR610580 20 40 42.2 Epon 828 0 40 40 0 GY281 0 0 0 42.2

pTHF is polytetrahydrofuran 250 (M.W. 250) available from AldrichChemical Co. (Milwaukee, Wis.).

UVR 6105 is an epoxy resin available from Union Carbide Co. (Danbury,Conn.).

Epon 828 is an epoxy resin available from Shell Chemical Co. (Houston,Tex.).

GY281 is a bisphenol F epoxy resin from Ciba Geigy.

An initiator solution was combined with one of the stock solutions toform a polymerizable resin solution by mixing the two solutions using aVertishear Cyclone I.Q. at 15,000 rpm for 40 minutes on ice forpolymerizable resin solutions are shown below. All amounts are given inw/w percent.

Polymerizable Resin Compositions

Component Resin B1 Resin B2 Resin B3 Resin B4 Resin B5 CD1012 1.25 1.251.25 1.25 20 CPQ 0.5 0.5 0.5 0.5 8 EDMAB 0 0 0.1 0.1 0 Stock A 98.2598.25 98.15 98.15 72 (A1) (A2) (A3) (A4) (A5) CD1012 is diaryliodoniumhexafluoroantimonate available from Sartomer (Exton, PA.). CPQ iscamphorquinone available from Aldrich Chemical Co. EDMAB isethyl-4-dimethyl aminobenzoate available from Aldrich Chemical Co.

CD1012 is diaryliodinium hexafluoroantimonate available from Sartomer(Exton, Pa.).

CPQ is comphorquinone available from Aldrich Chemical Co.

EDMAB is ethyl-4-dimethyl aminobenzoate available from Aldrich ChemicalCo.

Resin B6 is a vinyl ether -based composition prepared by mixing 0.5%(w/w) CPQ, 1.5% (w/w) CD1012, and 90% (w/w) Vectomer 4010 vinyl etherresin to form a stock solution, and then combining 99.5% (w/w) of thestock solution with 0.5% (w/w) para-dimethylamino benzoic acid.

Two gram composite samples for testing were prepared by handspatulation. Polymerizable resin composition B was weighed into a whiteplastic container and an appropriate amount of filler added using aMettler balance AE200 (Mettler Instrument Corp., Highstown, N.J.). Thesample was then mixed using a plastic stir rod until the filler waswell-dispersed in the resin (approximately 1–5 minutes). All effort wasmade to shield the sample from room light. All preparation and analysiswas performed under yellow lights to prevent photoinitiated reaction.

Composite samples were polymerized using visible, UV light, and/or heat.Visible light polymerization was done using a 3M Visilux 2θ which is afiltered lamp that emits light in the range of wavelengths ofapproximately 400 nm to 480 nm. Each sample was irradiated by placingthe lamp flush against the composite surface (covered in Mylar), placedon a mirror, for 120 seconds (60 seconds top and bottom).

In some examples, the sample was cured using UV light. In these cases,Sylvania 350 Black light bulbs F15T8/350BL (15 watt) and Fusion H and Dlight sources (Fusion Systems, Rockville, Md.) were used. The lightoutput (mJ/cm²) was measured using a Dynachem 500 UV IntegratedRadiometer (Tustin, Calif.).

Examples 1–4

These examples demonstrate the use of various screening tests to selectradiopacifying filler/resin/initiator combinations that, uponpolymerization, form a polymerized composition having a Barol hardness,measured according to Test Procedure A using the GYZJ-935 meter, of atleast 10 within 30 minutes following initiation of the cationicallyactive functional group at a reaction temperature of 25° C. Thescreening tests were developed by examining the interaction of bothradiopacifying and radiolucent fillers with various cationicallypolymerizable compositions. The fillers used in these examples wereprepared as follows:

Filler (a)

Filler sample (a) was prepared by heating Raysorb™ T3000 glass(ESS-Tech, Essington, Pa.) in a furnace at 600° C. for 18 hours.Raysorb™ T3000 is a barium aluminoborosilicate glass which according tothe vendor, contains 33% barium oxide.

Filler (b)

Filler sample (b) was Raysorb™ T3000 as received from the manufacturer.

Filler (c)–(e)

Filler samples (c)–(e) were prepared by a conventional melt process.Lanthanum oxide, silicon oxide, aluminum oxide, boric acid, and sodiumcarbonate were weighed out to yield the oxide compositions shown inTable 1. The batch ingredients were blended, charged to a platinumcrucible, heated to 1400–1500° C. for a sufficient time to assure ahomogeneous melt, quenched in water, and dried. The glass for samples(c) and (d) was crushed in an alumina plate grinder to yield frit lessthan approximately 2 mm diameter. The glasses for samples (c), (d), and(e) were milled in a porcelain jar mill with 0.5″ alumina media; 1 partby weight of ethanol per 99 parts glass was charged to the mill. Themilling time for sample (c) was 24 hr; for sample (d), 48 hr; for sample(e), 24 hr.

Filler (f)

Filler sample (f) was prepared as follows. 25.5 parts silica sol(“Ludox” LS: E.I. duPont de Nemours & Co.) were acidified by the rapidaddition of 0.255 parts concentrated nitric acid. In a separate vessel,12.9 parts ion-exchanged zirconyl acetate (Magnesium Elektron, Inc.)were diluted with 20 parts deionized water and the resultant solutionacidified with 0.255 parts concentrated nitric acid. The silica sol waspumped into the stirred zirconyl acetate solution and mixed for onehour. The stirred mixture was filtered through a 3 micrometer filterfollowed by a 1 micrometer filter. The filtrate was poured into trays toa depth of about 25 mm and dried at 65° C. in a forced air oven forabout 35 h. The resultant dried material was removed from the oven andtumbled through a rotary tube furnace (Harper Furnace Corp.) preheatedto 950° C. The calcined material was comminuted in a tumbling ball millwith ¼″ alumina media until an average particle size of 0.5–1.2micrometers (as measured on a Micromeritics 5100 sedigraph) is obtained;the mill charge included 75 parts calcined material, 3 parts methanol,1.9 parts benzoic acid, and 1. 1 parts deionized water. The filler wasthen loaded into ceramic saggers and fired in an electric furnace (L&LFurnace Corp.) in air at 880–900° C. for approximately 8 hr. The firedfiller was then ball-milled for 4–5 hr; the mill charge included 32parts fired filler, 1.25 parts ethanol, and 0.3 parts deionized water.Next the filler was passed through a 74 micrometer nylon screen in avibratory screener (Vortisiv V/S 10010); the filler was then blended ina V-blender (Patterson-Kelly Corp.) for about 15 min.

Filler (g)

Filler sample (g) was prepared as follows. Calcined material prepared asin sample (f) was comminuted in a tumbling ball mill with ¼″ aluminamedia until an average particle size of 1.1–1.8 micrometers (as measuredon a Micromeritics 5100 sedigraph) is obtained; the mill charge included94.4 parts calcined material, 1.4 parts methanol, and 4.1 partsdeionized water. The filler was then loaded into ceramic saggers andfired in an electric furnace (Harper Furnace Corp.) in air at 800–1000°C. for approximately 9 hr. The fired filler was then ball-milled for 4–5hr; the mill charge included 34 parts fired filler, 3.4 parts methanol,and 0.85 parts deionized water. Next the filler was passed through a 74micrometer nylon screen in a vibratory screener (Vortisiv V/S 10010);the filler was then blended in a V-blender (Patterson-Kelly Corp.) forabout 15 min.

Filler (h)

Filler sample (h) was prepared in the same way as filler sample (f),except that the firing condition was 1000° C. for 4 hr instead of880–900° C. for approximately 8 h. After firing, the filler was ballmilled with alumina media for 72 h; the charge included 900 partsfiller, 20 parts ethanol, and 5 parts deionized water. The mill wasopened at 24 h and 48 h, and any packed filler was dislodged.

Filler (i)

Filler sample (i) was prepared as follows. 1.42 parts by weight of boricacid (33906–7: Aldrich Chemical Company, Inc., Milwaukee) were added to19.87 parts of colloidal silica sol (1042: Nalco Chemical Company,Naperville) under vigorous stirring. After addition of 15.32 partsdeionized water, stirring was continued until the boric acid was fullydissolved. In another vessel 31.83 parts of zirconyl acetate (MagnesiumElektron, Inc.) was charged; under vigorous stirring 1.34 parts ACSgrade nitric acid was added to the zirconyl acetate. The colloidalsilica preparation was added to the zirconyl acetate preparation undervigorous stirring; stirring was continued for 1 hr. The sol was spraydried in a 3-ft. Niro spray drying unit with a rotary atomizer set at20,000 RPM; the resulting powder was fine and free-flowing. The spraydried powder was loaded into ceramic saggers and calcined in air in anelectric furnace (Cress Mfg. Company, El Monte, Calif.) according to theprofile: ramp to 200° C., soak for 1 hr, ramp to 550° C., hold for 4 hr,cool to room temperature. The powder was then ball-milled with ¼″alumina media for 32 hr; the charge included 260 parts by weight powder,6.5 parts benzoic acid, 10.4 parts methanol, and 4 parts deionizedwater. The resulting powder was then loaded into ceramic saggers andfired in air in an electric furnace (ramp to 900° C. at 14° C./min, holdfor 12 hr, cool to room temperature). The powder was then ball-milledfor 24 hr with ¼″ alumina media; the charge included 400 parts by weightof powder, 4 parts of ethanol, and 1 part of deionized water.

Filler (j)

Filler sample (j) was prepared in the same manner as (i) except that thefiring temperature was 750° C. instead of 900° C.

Filler (k)

Filler sample (k) was prepared in the same manner as (i) except that thefiring temperature was 850° C. instead of 900° C.

Filler (l)

Filler sample (l) was prepared as follows. A portion of filler sample(m) was loaded into ceramic saggers and fired in air in an electricfurnace (Cress Mfg. Company, El Monte, Calif.) according to the profile:ramp to 1000° C., hold for 4 hr, cool to room temperature. The fillerwas then ball-milled for 24 hr with ¼″ alumina media; the chargeincluded 1145 parts by weight of filler, 40 parts of ethanol, and 10part of deionized water.

Filler (m)

Filler sample (m) was prepared as follows. 19.297 parts by weight ofaluminum formoacetate (“AFA”) were charged to a vessel. The AFA wasprepared as follows. A flask was charged with 400 g of deionized water,34.5 ml of glacial acetic acid, and 25.6 ml of concentrated formic acid.The resulting solution was brought to a roiling boil, after which 26.98g of aluminum metal powder were added in three portions of roughly 9 geach over a 2 hour period. An exothermic reaction ensued after theinitial addition, and the rate of the reaction was moderated by theaddition of room temperature deionized water. The digestion wascontinued for 10 h, after which the solution was cooled and filtered toyield 9.25 wt. % of Al₂O₃ (pH=4.45).

In a separate vessel a solution of 1 part by weight of lanthanum nitratehexahydrate to 1 part deionized water was prepared. Under vigorousstirring, 16.347 parts of the lanthanum nitrate hexahydrate solution wasadded to the aluminum formoacetate preparation and stirred for 1 hr.7.647 parts of colloidal silica sol sol (1042: Nalco Chemical Company,Naperville) was added to the preparation under vigorous stirring, andstirred for 1 hr. 1.208 parts of ACS grade nitric acid was added to thepreparation under vigorous stirring, and stirred for 20 min. The sol wasspray dried in a 3-ft. Niro spray drying unit with a rotary atomizer setat 20,000 RPM; the resulting powder was fine and free-flowing. The spraydried powder was loaded into ceramic saggers and calcined in air in anelectric furnace (Cress Mfg. Company, El Monte, Calif.) according to theprofile: ramp to 200° C., soak for 1 hr, ramp to 550° C., hold for 4 hr,cool to room temperature. The powder was then ball-milled with ¼″alumina media for 6 hr; the charge included 900 parts by weight powderand 4 parts deionized water.

Filler (n)

Filler sample (n) was prepared as follows. Quartz rock was heated toabout 660° C., quenched in water, drained, then dried in a forced airoven for 16 hours at about 200° F. The quenched quartz was combined withquartz media into a mill and tumbled for about 70 hours; the chargeincluded 99 parts by weight quenched quartz and 1 part methanol. Theresulting particles were blended with 0.1 wt. % carbon black in aV-blender for 1 hour, then fired in an electric furnace at about 950° C.for 4 hours. The resulting particles were passed through a 100micrometer nylon screen, then blended in a V-blender for 30 minutes.

Filler (o)

Filler sample (o) was prepared as follows. Fused quartz tubing of 1 mmwall thickness was broken into shards with a hammer before ball-millingwith 0.5 inch alumina media for 24 hour; the charge contained 99 partsby weight of the shards and 1 part ethanol.

Filler (p)

Filler (p) was a commercially available calcium carbonate filler (Huber)Quincy, Ill.

Filler (q)

Filler (q) was a commercially available calcium carbonate filler (ECCInternational, Sylacauga, Ala.).

Filler (r)

Filler (r) was a commercially available feldspar filler (The FeldsparCorp., Atlanta, Ga.).

Filler (s)

Filler (s) was KBF₄ obtained from Atotech of Rock Hill, S.C.

Filler (t)

Filler (t) was a melt-derived cryolite filler obtained from TarconordA/A, Avernakke, Denmark.

Filler (u)

Filler (u) was a synthetic cryolite obtained from Kali-Chemie Corp.,Greenwich, Conn.

Filler (v)

Filler (v) was a treated titanium dioxide obtained from DuPont(Wilmington, Del.) (IT-Pure Series).

Filler (w)

Filler (w) was a blend of 30% (w/w) filler (f) and 40% (w/w) filler (n).

Filler (x)

Filler (x) was a blend of 9% (w/w) ytterbium trifluoride (AldrichChemical Co.) and 61% (w/w) filler (n).

The chemical compositions of fillers (a)–(m) are summarized below inTable 1. All amounts are given in weight percent. In the case of fillers(a) and (b), the amount of BaO is based upon information reported by thevendor.

TABLE 1 Filler Al2O3 B2O3 BaO La2O3 SiO2 ZrO2 Other (a) 33 (b) 33 (c) 2020 30 30 (d) 20 20 30 30 (e) 20 20 20 30 10 Na20 (f) 72.8 27.2 (g) 72.827.2 (h) 72.8 27.2 (i) 5.4 45.9 48.7 (j) 5.4 45.9 48.7 (k) 5.4 45.9 48.7(l) 35.7 12.3 52 (m) 35.7 12.3 52

Fillers (a)–(v) were characterized according to Test Procedures G–M. Theresults are summarized below in Table 2. The designation “—” means nottested.

In the case of the particle size data, the figure in parenthesesrepresents the standard deviation. The letters B, M, and T reflect theparticle size distribution and correspond to Mono-modal, Biomodal, andTrimodal, respectively.

TABLE 2 Particle Sp. Karl Fluores- BET size Gravity Fisher Filler n_(D)XRD cence (m²/g) (μm) (g/cc) (%) (a) 1.546 — N 1.45 2.132 3.0147 0.02(3.221)B (b) 1.553 — N 1.60 3.731 2.9744 0.0037 (5.604)B (c) 1.585 — N3.35 5.402 2.9984 0.04 (4.680)B (d) 1.585 — N 3.57 1.906 3.0774 0.066(2.570)T (e) — — N 1.90 13.18 2.7732 0.15 (f) 1.542 — N 54.55 2.3472.6877 0.24 (3.714)B (g) 1.542 — N 10.65 1.019 2.7080 0.12 (1.072) (h) —— — 68.93 0.799 2.6902 0.28 (0.608)M 0.80 (i) 1.542 — — 14.99 0.8373.273 0.25 (j) — — — 51.14 1.179 3.0477 0.66 ((2.109)B (k) — — — 13.510.649 3.1395 0.35 (0.358)M (l) 1.533 — — 32.47 4.019 2.639 0.25 (4.838)B(m) 1.528 AM W/B 165.74 11.830 2.5094 3.46 (7.644)B (n) 1.544 — — 6.703.328 2.6267 0.078 (5.219)B (o) 1.459 — — 2.92 1.017 2.2871 0.042(0.789)B (p) 1.57  — — 1.04 16.55 2.737 0.08 (q) 1.57  — — 3.03 5.662.740 0.05 (r) 1.537 — — 1.07 20.19 2.635 0.04 (s) 1.325 — — 0.48 20.702.517 0.03 (t) 1.34  — — 1.03 17.69 3.00 0.04 (u) 1.34  — — 0.46 13.712.875 0.02 (v) — — — — 0.781 — — (0.297)M

Example 1

This example demonstrates that the isoelectric point may be used as ascreening test. Isoelectric points for various filler compositions weredetermined according to Test Procedure B. Samples for hardness testingwere prepared at 50% (w/w) and 70% (w/w) filler loading according to thegeneral procedure described above. The resin in each case was Resin B2.Samples were cured with visible light using a 3M Visilux 2™ light. Thesample was irradiated by placing the lamp flush against the compositesurface (covered with Mylar) for 120 seconds (60 seconds on both top andbottom). The composite was placed against a mirror during curing.

Hardness was evaluated according to Test Procedure A. The results aresummarized in tabular form in Tables 3A and 3B. “No cure” meant that thecomposite did not register on either of the two hardness meters, i.e.,when the Mylar film was removed from the mold, the uncured resin pulledaway with the film or was easily penetrated. The results using theGYZJ-935 meter are also shown graphically in FIGS. 1( a) (50% (w/w)filler loading) and 1(b) (70% (w/w) filler loading). A Barcol value of−5 denotes no cure.

These results demonstrate that, in general, for filler loadings of 50%(w/w) or greater, radiopacifying fillers having isoelectric points nogreater than 7 can be used successfully.

There were some fillers (fillers (f), (h), (v) at 50% loading andfillers (b), (f), (h), and (v) at 70% loading ) which did notsuccessfully polymerize even though they had IEP values no greater than7. However, these fillers did satisfy other screening tests, asdescribed below. These results demonstrate that the individual screeningtests preferably should be used in combination with each other for thebest results.

TABLE 3A 50% (w/w) Filler Filler IEP GYZJ-934-1 GYZJ-935 (a) 2.8 18 82(b) 3.1 22 88 (c) 6.4 22 88 (d) 6.5 28 82 (e) NA No Cure No Cure (f) 2.2No Cure No Cure (g) 2.4 22 82 (h) 3.6 No Cure No Cure (i) 2.2  8 82 (j)3.9 18 88 (k) 4.1 18 82 (l) 5.5 22 88 (m) 7.6 No Cure No Cure (n) 1.2 4298 (o) 2.5 32 92 (p) 9.5 No Cure No Cure (q) 9.5 No Cure No Cure (r) 2  32 92 (s) — 22 82 (t) 4.5 22 88 (u) 5.5 22 88 (v) 6.9 — —

TABLE 3B 70% (w/w) Filler Filler IEP GYZJ-934-1 GYZJ-935 (a) 2.8 25 95(b) 3.1 No Cure No Cure (c) 6.4 50 95 (d) 6.5 25 95 (e) NA No Cure NoCure (f) 2.2 No Cure No Cure (g) 2.4  0  0 (h) 3.6 No Cure No Cure (i)2.2 30 95 (j) 3.9  0 95 (k) 4.1  5 90 (l) 5.5 35 95 (m) 7.6 No Cure NoCure (n) 1.2 50 95 (o) 2.5 40 100  (p) 9.5 No Cure No Cure (q) 9.5 NoCure No Cure (r) 2    0 85 (s) — 20 90 (t) 4.5  0 90 (u) 5.5 30 85 (v)6.9 — No Cure

Example 2

This example demonstrates that adsorption isotherm analysis may be usedas a screening test. Adsorption values for various filler compositionswere determined according to Test Procedure C. Samples for hardnesstesting were prepared at 50% (w/w) and 70% (w/w) filler loading as inExample 1. The resin in each case was Resin B2.

The absorption value (Γ′) is reported in μmoles/g filler as the observedadsorption multiplied by the B.E.T. surface area of the filler (seeTable 2).

Hardness was evaluated as in Example 1. The results are summarized intabular form in Tables 4A and 4B. The results using the GYZJ-935 meterare also shown graphically in FIGS. 2( a) (50% (w/w) loading) and 2(b)(70% (w/w)loading). A Barcol value of −5 denotes no cure.

These results demonstrate that, in general, for filler loadings of 70%(w/w), filler compositions exhibiting adsorption values of no greaterthan about 20 micromoles/g filler, measured as described above, can beused successfully. For filler loadings between 50 and 70% (w/w), fillercompositions having adsorption values no greater than 80 micromoles/gfiller can be used.

Filler (t) at 50% and 70% (w/w) loading met the minimum Barcol hardnesslevel even though its adsorption value was greater than 80 micromoles/gfiller. Conversely, filler (g) at 70% (w/w) loading did not meet theminimum Barcol hardness value even though it had an adsorption valueless than 80 micromoles/g filler. This demonstrates that the individualscreening tests preferably should be used in combination with each otherfor the best results.

TABLE 4A 50% (w/w) Filler Filler Γ′ (

moles/g) GYZJ-934-1 GYZJ-935 (a) 8.63 18 82 (b) 27.33 22 88 (c) 7.19 2288 (d) 5.75 28 82 (e) 86.29 No Cure No Cure (f) 86.29 No Cure No Cure(g) 11.51 22 82 (h) 86.29 No Cure No Cure (i) 8.63  8 82 (j) 10.35 18 88(k) 12.94 18 82 (l) 10.35 22 88 (m) — No Cure No Cure (n) 5.75 42 98 (o)7.19 32 92 (p) 86.29 No Cure No Cure (q) 86.29 No Cure No Cure (r) 12.6632 92 (s) 8.92 22 82 (t) 86.29 22 88 (u) 8.63 22 88 (v) — — — (w) 86.29— — (x) 8.63 — —

TABLE 4B 70% (w/w) Filler Filler Γ′ (

moles/g) GYZJ-934-1 GYZJ-935 (a) 8.63 25 95 (b) 27.33 No Cure No Cure(c) 7.19 50 95 (d) 5.75 25 95 (e) 86.29 No Cure No Cure (f) 86.29 NoCure No Cure (g) 11.51  0  0 (h) 86.29 No Cure No Cure (i) 8.63 30 95(j) 10.35  0 95 (k) 12.94  5 90 (l) 10.35 35 95 (m) — No Cure No Cure(n) 5.75 50 95 (o) 7.19 40 100  (p) 86.29 No Cure No Cure (q) 86.29 NoCure No Cure (r) 12.66  0 85 (s) 8.92 20 90 (t) 86.29  0 90 (u) 8.63 3085 (v) — — No Cure (w) 86.29 No Cure No Cure (x) 8.63 40 —

Example 3

This example demonstrates that conductivity may be used as a screeningtest. Conductivity values for test solutions containing fillercompositions were determined according to Test Procedure D. Samples forhardness testing were prepared at 50% (w/w) and 70% (w/w) filler loadingas described in Example 1. The resin in each case was Resin B2.

Hardness was evaluated as described in Example 1. The results aresummarized in tabular form in Tables 5A and 5B. The results using theGYZJ-935 meter are also shown graphically in FIGS. 3( a) (50% (w/w)filler loading) and 3(b) (70% (w/w) filler loading). A Barcol value of−5 denotes no cure.

These results demonstrate that, in general, for filler loading of 70%(w/w), fillers causing conductivity changes no greater than 60 mV can beused successfully. In the case of filler loadings of 50% (w/w), fillerscausing conductivity changes no greater than 125 mV can be usedsuccessfully.

TABLE 5A Conductivity 50% (w/w) Filler Filler Change (mV) GYZJ-934-1GYZJ-935 (a) 19.2 18 82 (b) 90.2 22 88 (c) 10.4 22 88 (d) 8.4 28 82 (e)207.5 No Cure No Cure (f) 156.0 No Cure No Cure (g) 65.8 22 82 (h) 140.6No Cure No Cure (i) 19.4  8 82 (j) 41.0 18 88 (k) 21.5 18 82 (l) 47.3 2288 (m) 248.1 No Cure No Cure (n) −6.4 42 98 (o) 0.8 32 92 (p) 131.3 NoCure No Cure (q) 218.4 No Cure No Cure (r) 41.4 32 92 (s) 35.1 22 82 (t)11.9 22 88 (u) 15.7 22 88 (w) 122 — — (x) −3 — —

TABLE 5B Conductivity 70% (w/w) Filler Filler Change (mV) GYZJ-934-1GYZJ-935 (a) 19.2 25 95 (b) 90.2 No Cure No Cure (c) 10.4 50 95 (d) 8.425 95 (e) 207.5 No Cure No Cure (f) 156.0 No Cure No Cure (g) 65.8  0  0(h) 140.6 No Cure No Cure (i) 19.4 30 95 (j) 41.0  0 95 (k) 21.5  5 90(l) 47.3 35 95 (m) 248.1 No Cure No Cure (n) −6.4 50 95 (o) 0.8 40 100 (p) 131.3 No Cure No Cure (q) 218.4 No Cure No Cure (r) 41.4  0 85 (s)35.1 20 90 (t) 11.9  0 90 (u) 15.7 30 85 (w) 121.5 — No Cure (x) −3 40 —

Example 4

This example demonstrates that FTIR spectroscopy, using ethyl acetate asa standard, may be used as a screening test in the case ofsol-gel-derived fillers. Percent peak height values for test solutionscontaining filler compositions were determined according to TestProcedure E. Samples for hardness testing were prepared at 50% (w/w) and70% (w/w) filler as described in Example 1. The resin in each case wasResin B2.

Hardness was evaluated as described in Example 1. The results aresummarized in tabular form in Tables 6A and 6B. The results using theGYZJ-935 meter are also shown graphically in FIGS. 4( a) (50% (w/w)filler loading) and 4(b) (70% (w/w) filler loading). A Barcol value of−5 denotes no cure.

The results demonstrate that in general, filler compositions having anFTIR peak height relative to ethyl acetate of greater than 80% can beused successfully.

Filler (j) at both 50% and 70% loading successfully polymerized eventhough its % peak height value was less than 80%. Conversely, filler (g)at 70% loading did not meet the minimum Barcol hardness value eventhough its % peak height value was greater than 80%. These resultsdemonstrate that the individual screening tests preferably should beused in combination with each other for the best results.

TABLE 6A 50% (w/w) Filler Filler % Peak Height GYZJ-934-1 GYZJ-935 (f)75.7 No Cure No Cure (g) 95.1 22 82 (h) 49.9 No Cure No Cure (i) 94.6  882 (j) 35.9 18 88 (k) 99.4 18 82 (l) 88.2 22 88 (m) 2.7 No Cure No Cure

TABLE 6B 70% (w/w) Filler Filler % Peak Height GYZJ-934-1 GYZJ-935 (f)75.7 No Cure No Cure (g) 95.1  0  0 (h) 49.9 No Cure No Cure (i) 94.6 3095 (j) 35.9  0 95 (k) 99.4  5 90 (l) 88.2 35 95 (m) 2.7 No Cure No Cure

Examples 5–44

These examples demonstrate the successful preparation of a number ofcationically polymerized compositions using various radiopacifyingfiller compositions. The various fillers were prepared as follows:

Example 5

The filler sample was a commercially available strontiumaluminoborosilicate glass, Raysorb™ T4000 (Ess-Tech, Essington, Pa.).

Example 6

The filler sample was a commercially available bariumaluminoborosilicate glass, Schott GM-27884 (Schott Glaswerke, Landshut,Germany); the composition reported by the vendor is shown in Table 7.

Example 7

The filler sample was prepared by ball milling a commercial bariumaluminoborosilicate glass, Coming 7724 (Coming Glass Works, Coming,N.Y.) with alumina media for 3 hours. The milled glass was then heatedat 600° C. for 18 h.

Example 8

The filler sample was prepared by a conventional melt process.Appropriate precursors were weighed out to yield the oxide compositionshown in Table 7. After blending, the batch was heated to 1400–1500° C.for a sufficient time to assure a homogeneous melt, quenched in water,and dried. The glass frit was then ball milled.

Example 9

The filler sample was prepared by milling a glass frit in an aluminamill in a Spex 8000 unit (Spex Industries, Edison, N.J.) for 10 min. Theglass frit was prepared by weighing out appropriate precursors to yieldthe oxide composition shown in Table 7. After blending, the batch washeated to 1400–1650° C. for a sufficient time to assure a homogeneousmelt, quenched in water, and dried.

Example 10

The filler sample was prepared by milling a glass frit, prepared asdescribed in Example 9, in an alumina mill in the Spex 8000 for 30 min;the fillers were then sieved with a 400 micrometer nylon screen.

Example 11

The filler sample was prepared by milling a glass frit, prepared asdescribed in Example 9, in an alumina mill in the Spex 8000 for 20 min.

Example 12

The filler sample was prepared by milling a glass frit, prepared asdescribed above in Example 9, in a ball mill with alumina media for 24hours; the powder was then heated to 600° C. for 24 hours.

Example 13

The filler sample was prepared by milling a glass frit, prepared asdescribed in Example 9, in an alumina mill in the Spex 8000 for 30 min;the fillers were then sieved with a 400 micrometer nylon screen.

Example 14

The filler sample was prepared by milling a glass frit, prepared asdescribed in Example 9, in an zirconia mill in the Spex 8000 for 10 min.

Example 15

The filler sample was prepared by ball milling a glass frit, prepared asdescribed in Example 9, with alumina media; the mill charge included 600parts by weight glass frit and 6 parts ethanol.

Example 16

The filler sample was prepared by milling a glass frit, prepared asdescribed in Example 9, in an alumina mill in the Spex 8000 for 20 min.

Example 17

The filler sample was prepared by ball-milling a glass frit, prepared asdescribed in Example 9, with alumina media for 24 h; the milled fillerwas then sieved through a 60 micrometer nylon screen.

Example 18

21.39 parts by weight of nitric acid was added to 1071.3 parts ofcolloidal silica sol (Nalco 1042: Nalco Chemical Co.) under vigorousstirring. In another vessel, 12.58 parts of nitric were added to 616.1parts zirconyl acetate (Magnesium Elektron, Inc.) under vigorousstirring. Next, the zirconyl acetate preparation was slowly added to thecolloidal silica preparation under vigorous stirring. The resulting solwas spray dried in a Niro 3-ft. spray dryer; the resulting powder wasfine and free-flowing. The powder was calcined at 500° C. for 4 h, thenball-milled with alumina media; the mill charge included 75 partscalcined material, 3 parts methanol, 1.9 parts benzoic acid, and 1.1parts deionized water. The filler was then fired at 1000° C. for 4 h.

Example 19

8.9 parts by weight of boric acid was dissolved in 1058 parts by weightof colloidal silica sol (Nalco 1042: Nalco Chemical Co.) under vigorousstirring. In another vessel, 32.23 parts of nitric acid was added to616.5 parts of zirconyl acetate under vigorous stirring. Next, thezirconyl acetate preparation was slowly added to the colloidal silicapreparation under vigorous stirring. The resulting sol was spray driedin a Niro 3-ft. spray dryer; the resulting powder was fine andfree-flowing. The powder was calcined at 500° C. for 4 h, thenball-milled with alumina media; the mill charge included 75 partscalcined material, 3 parts methanol, 1.9 parts benzoic acid, and 1.1parts deionized water. The filler was then fired at 1000° C. for 4 h.

Example 20

44.5 parts by weight of boric acid was dissolved in 998 parts by weightof colloidal silica sol (Nalco 1042: Nalco Chemical Co.) under vigorousstirring. In another vessel, 29.03 parts of nitric acid was added to616.8 parts of zirconyl acetate under vigorous stirring. Next, thezirconyl acetate preparation was slowly added to the colloidal silicapreparation under vigorous stirring. The resulting sol was spray driedin a Niro 3-ft. spray dryer; the resulting powder was fine andfree-flowing. The powder was calcined at 500° C. for 4 h, thenball-milled with alumina media; the mill charge included 75 partscalcined material, 3 parts methanol, 1.9 parts benzoic acid, and 1.1parts deionized water. The filler was then fired at 900° C. for 4 h. Avial of the compounded sol was stored under ambient conditions; the soldisplayed no gelling or precipitation after 2.5 years.

Example 21

1.33 parts by weight of boric acid (33906-7: Aldrich Chemical Company,Inc., Milwaukee) were added to 29.9 parts of colloidal silica sol (1042:Nalco Chemical Company, Naperville) under vigorous stirring. Afteraddition of 13.2 parts deionized water, stirring was continued until theboric acid was fully dissolved. In another vessel 18.63 parts ofzirconyl acetate (Magnesium Elektron, Inc.) was charged; under vigorousstirring 0.97 parts ACS grade nitric acid was added to the zirconylacetate. The colloidal silica preparation was added to the zirconylacetate preparation under vigorous stirring; stirring was continued for1 hr. The sol was spray dried in a 3-ft. Niro spray drying unit with arotary atomizer set at 20,000 RPM; the resulting powder was fine andfree-flowing. The spray dried powder was loaded into ceramic saggers andcalcined in air in an electric furnace (Cress Mfg. Company, El Monte,Calif.) according to the profile: ramp to 200° C., soak for 1 hr, rampto 550° C., hold for 4 hr, cool to room temperature. The powder was thenball-milled with ¼″ alumina media for 65 hr; the charge included 130parts by weight powder, 3 parts benzoic acid, 5 parts methanol, and 2parts deionized water. After blending in a V-blender (Patterson-Kelly)for 30 min, the powder was loaded into ceramic saggers and fired in airin an electric furnace (ramp to 900° C., hold for 12 hr, cool to roomtemperature). The powder was then ball-milled for 24 hr with ¼″ aluminamedia; the charge included 400 parts by weight of powder, 4 parts ofethanol, and 1 part of deionized water.

Example 22

18.59 parts by weight of nitric acid was added to 856.3 parts deionizedwater; this solution was then added to 1071.3 parts of colloidal silicasol (Nalco 1042: Nalco Chemical Co.) under vigorous stirring. 88.1 partsof boric acid was then added under vigorous stirring. In another vessel12.58 parts of nitric acid were added to 616.1 parts zirconyl acetate(Magnesium Elektron, Inc.) under vigorous stirring. Next, the zirconylacetate preparation was slowly added to the colloidal silica preparationunder vigorous stirring. The resulting sol was spray dried in a Niro3-ft. spray dryer; the resulting powder was fine and free-flowing. Thepowder was calcined at 500° C. for 4 h, then ball-milled with aluminamedia; the mill charge included 75 parts calcined material, 3 partsmethanol, 1.9 parts benzoic acid, and 1.1 parts deionized water. Thefiller was then fired at 800° C. for 4 h. A vial of the compounded solwas stored under ambient conditions; the sol displayed no gelling orprecipitation after 2.5 years.

Example 23

7.0 parts by weight of nitric acid was added to 1414 parts deionizedwater; this solution was then added to 389 parts of colloidal silica sol(Nalco 1042: Nalco Chemical Co.) under vigorous stirring. 88.1 parts ofboric acid was then added under vigorous stirring. In another vessel 6.0parts of nitric acid were added to 308 parts zirconyl acetate (MagnesiumElektron, Inc.) under vigorous stirring. Next, the zirconyl acetatepreparation was slowly added to the colloidal silica preparation undervigorous stirring. The resulting sol was spray dried in a Niro 3-ft.spray dryer; the resulting powder was fine and free-flowing. The powderwas calcined at 500° C. for 4 h, then ball-milled with alumina media;the mill charge included 75 parts calcined material, 3 parts methanol,1.9 parts benzoic acid, and 1.1 parts deionized water. A vial of thecompounded sol was stored under ambient conditions; the sol displayed nogelling or precipitation after 2.5 years.

Example 24

11 parts by weight of AFA was charged to a vessel. Under vigorousstirring were then added 64.5 parts of a solution of 23.3 parts boricacid dissolved in 466.6 parts deionized water, 21.4 parts zirconylacetate (Magnesium Elektron, Inc.), 36.9 parts of colloidal silica sol(1034A: Nalco Chemical Co.), and 16.3 parts glacial acetic acid. The solwas stirred for 3 days, then spray dried in a Bηchi spray dryer. Thepowder was calcined at 500° C. for 4 h, then fired at 1050° C. for 2 h.

Example 25

140 parts by weight of lanthanum nitrate hexahydrate (12915: Alfa Aesar,Ward Hill, Mass.) was dissolved in 120 parts deionized water. 97 partsof colloidal silica sol (1034A: Nalco Chemical Co.) were added to 83.9parts of the lanthanum nitrate solution under vigorous stirring. Theresulting sol was poured into a Pyrex™ tray and placed in an oven at 55°C. for 2 days; the dried gel was then milled in an alumina mill in aSpex 8000 unit (Spex Industries, Edison, N.J.) for 5 min. The powder wasthen fired at 1050° C. for 2 h.

Example 96

889 parts by weight of lanthanum nitrate hexahydrate was dissolved in902 parts of deionized water. 34.2 parts of colloidal silica sol (1034A:Nalco Chemical Co.) was added to 43.2 parts of the lanthanum nitratesolution under vigorous stirring. The resulting sol was poured into aPyrex™ tray and dried at 55° C. to a coarse particulate gel. The driedgel was calcined at 550° C. for 3 h, manually crushed to a powder in analumina mortar and pestle, then fired at 1050° C. for 2 h.

Example 27

965 parts by weight of AFA was charged to a beaker; under vigorousstirring were then added 158 parts of a solution of 889 parts lanthanumnitrate hexahydrate in 902 parts deionized water, followed by 383 partsof colloidal silica sol (1034A: Nalco Chemical Co.). The resulting solwas spray dried in a Niro 3-ft. spray dryer. The resulting powder wascalcined at 550° C. for 4 h, then ball milled with ¼″ alumina media; thecharge included 130 parts by weight powder, 3 parts benzoic acid, 5parts methanol, and 2 parts deionized water. The filler was fired at1000° C. for 4 h. The fired filler was ball milled with ¼″ aluminamedia; the charge included 130 parts of filler, 5.2 parts ethanol, and1.3 parts water.

Example 28

128.4 parts by weight of deionized water was added to 99.5 parts ofcolloidal silica sol (1034A: Nalco Chemical Co.) under vigorous stirringand low heat; 20.0 parts of boric acid (339067: Aldrich Chemical Co.)was added; 113.4 parts of deionized water was added. Vigorous stirringcontinued throughout until all powder was dissolved. In a separatevessel 674.3 parts of lanthanum nitrate hexahydrate was dissolved in 809parts deionized water; next, 29.4 parts of the lanthanum nitratesolution was added to the colloidal silica preparation. The resultingsol was diluted by 1 part by weight sol per 2 parts deionized water, andthen spray dried on a Niro 3-foot spray dryer. After calcining at 500°C. for 4 h, the powder was fired at 850° C. for 2 h; the resultingpowder was free flowing.

Example 29

100 parts by weight of deionized water was added to 111.7 parts ofcolloidal silica sol (1034A: Nalco Chemical Co.) under vigorous stirringand low heat; 8.9 parts of boric acid (339067: Aldrich Chemical Co.) wasadded; vigorous stirring was continued until all powder was dissolved.In a separate vessel 674.3 parts of lanthanum nitrate hexahydrate wasdissolved in 809 parts deionized water; next, 41.0 parts of thelanthanum nitrate solution was added to the colloidal silicapreparation. The resulting sol was diluted by 1 part by weight sol per 2parts deionized water, and then spray dried on a Niro 3-foot spraydryer. After calcining at 500° C. for 4 h, the powder was fired at 850°C. for 2 h; the resulting powder was free flowing.

Example 30

The filler sample was prepared identically to the filler sample ofExample 29 except that the firing temperature was 1050° C. instead of850° C.

Example 31

2.7 parts of boric acid (339067: Aldrich Chemical Co.) was added to111.7 parts of colloidal silica sol (1034A: Nalco Chemical Co.) undervigorous stirring and low heat until all powder was dissolved. In aseparate vessel 674.3 parts of lanthanum nitrate hexahydrate wasdissolved in 809 parts deionized water; next, 48.0 parts of thelanthanum nitrate solution was added to the colloidal silicapreparation. The resulting sol was diluted by 1 part by weight sol per 2parts deionized water, and then spray dried on a Niro 3-foot spraydryer. After calcining at 500° C. for 4 h, the powder was fired at 850°C. for 2 h; the resulting powder was free flowing.

Example 32

The filler sample was prepared identically to the filler sample ofExample 31 except that the firing temperature was 1050° C. instead of850° C.

Example 33

The filler sample was prepared identically to the filler sample ofExample 31 except that the firing temperature was 1200° C. instead of850° C.

Example 34

4.43 parts by weight of boric acid (339067: Aldrich Chemical Co.) wasdissolved fully in 97 parts of colloidal silica sol (1034A: NalcoChemical Co.) under vigorous stirring and low heat. In another vessel140 parts by weight of lanthanum nitrate hexahydrate (12915: Alfa Aesar,Ward Hill, Mass.) was dissolved in 120 parts deionized water. 70.9 partsof the lanthanum nitrate solution was added to the colloidal silicapreparation under low heat and vigorous stirring. About 25 ml of theresulting sol was poured into a Pyrex™ beaker and heated in a microwaveoven (Model R-9H83: Sharp Electronics Corp., Mahwah, N.J.) for 9 min;the result was an opaque, moist gel. This gel was calcined at 550° C.for 2.5 h, then milled in an alumina mill in the Spex 8000 for 2 min.

Example 35

Sol prepared identically to the filler sample of Example 34 was pouredinto a tray and dried at 60° C. for three days; the dried gel was thenmilled in an alumina mill in the Spex 8000 for 20 min. The milled powderwas heated to 500° C. for 2 h, then heated to 900° C. for 4 h.

Example 36

173 parts by weight of AFA was charged to a vessel. Under vigorousstirring, the following ingredients were added, one at a time: 53 partscolloidal silica sol (1034A: Nalco Chemical Co.), 263.3 parts of asolution of 674.3 parts lanthanum nitrate hexahydrate and 809.4 partsdeionized water, 28.4 parts boric acid. Stirring was continued until thepowder was completely dissolved. The sol was spray dried in a Buchispray dryer. The resulting powder was calcined at 500° C. for 45 min,then at 800° C. for about 14 h. The powder was fired at 850° C. for 6 h.

Example 37

Spray dried powder prepared as described in Example 38 (below) wascalcined at 500° C. for 2:45 h, and then milled in an alumina mill in aSpex 8000 unit (Spex Industries, Edison, N.J.) for 5 min.

Example 38

86.5 parts by weight of AFA was charged to a vessel. Under vigorousstirring, the following ingredients were added, one at a time: 33.9parts colloidal silica sol (1034A: Nalco Chemical Co.), 131.6 parts of asolution of 674.3 parts lanthanum nitrate hexahydrate and 809.4 partsdeionized water, 14.2 parts boric acid. Stirring was continued until thepowder was completely dissolved. The sol was spray dried in a Buchispray dryer. The resulting powder was calcined at 500° C. for 45 min,then at 800° C. for about 14 h. The powder was fired at 850° C. for 6 h.

Example 39

Under vigorous stirring, 38.4 parts of a solution of yttrium nitratehexahydrate in deionized water yielding 15.7 wt % of yttrium oxide wasadded to 26.6 parts of colloidal silica sol sol (1034A: Nalco ChemicalCo.); several drops of nitric acid was added to reduce the pH from about4–5 to 0–0.5. The sol was poured into a Pyrex™ beaker, then heated in amicrowave oven for 14 min. The resulting dried gel was fired at 1000° C.for 2 h, then ground manually in an alumina mortar and pestle to apowder.

Example 40

48.7 parts by weight of AFA was charged to a vessel. Under vigorousstirring, 28.8 parts of a solution of yttrium nitrate hexahydrate indeionized water, yielding 15.7 wt % of yttrium oxide, was added to 17.9parts of colloidal silica sol sol (1034A: Nalco Chemical Co). The solwas poured into a Pyrex™ beaker, then heated in a microwave oven for 19min. The resulting dried gel was fired at 1000° C. for 2 h, then groundmanually in an alumina mortar and pestle to a powder.

Example 41

Approximately 4.86 kg of Nalco 2326 silica sol (a silica sol of 14.5 wt% solids, pH of 9.0, ammonium ion stabilized) was mixed with 6.02 kg ofwater. To this was added a mixture of 1.34 kg Nyacol 10/20 Zirconia sol(a zirconia sol of 20 wt % solids, pH of 0.5, nitrate ion stabilized)with 1.48 kg of water containing 30 g of boric acid pre-dissolved in it.This resulted in a sol which, on a solids weight basis, is approximately70% silica, 27% zirconia, and 3% boric acid.

This sol was subsequently spray dried, at 30,000 R.P.M. on a Niro 3 ft.spray dryer, an inlet temperature of approximately 200° C., and anoutlet temperature of 100° C. The resulting powder was then fired at1000° C. for 6 hours.

Example 42

Approximately 5.03 kg of Nalco 2326 silica sol (a silica sol of 14.5 wt% solids, pH of 9.0, ammonium ion stabilized) was mixed with 5.06 kg ofwater. To this was added a mixture of 1.34 kg Nyacol 10/20 Zirconia sol(a zirconia sol of 20 wt % solids, pH of 0.5, nitrate ion stabilized)with 1.36 kg of water. This resulted in a sol which, on a solids weightbasis, is approximately 73% silica and 27% zirconia.

This sol was subsequently spray dried, at 30,000 R.P.M., on a Niro 3 ft.spray dryer an inlet temperature of approximately 200° C., and an outlettemperature of 100° C. The resulting powder was then fired at 1000° C.for 6 hours. When evaluated according to Test Procedure E, the fillerexhibited a % peak height of 100.

Example 43

Nyacol 10/20 Zirconia sol (a zirconia sol of 20 wt % solids, pH of 0.5,nitrate ion stabilized) was dried in an oven at 140° C. overnight toremove water. The sample was then crushed by hand using a mortar &pestle to break up loose agglomerates.

The resulting powder was fired at 1000° C. to remove any residualnitrates. When evaluated according to Test Procedure E, the fillerexhibited a % peak height of 100.

Example 44

The filler sample was prepared identically as described in Example 20except that the sample was fired at 800° C. for 4 hours.

The chemical compositions of the fillers used in Examples 5–44 aresummarized below in Table 7. All amounts given are in weight %.

TABLE 7 Example Al2O3 B2O3 BaO La2O3 SiO2 Y2O3 ZnO ZrO2 Other 5 — — — —— — — — — 6 10 10 25 — 55 — — — — 7 — — — — — — — — — 8 15 9 4.5 — 50 —21 — 0.5F 9 14.65 9.09 4.55 — 50.5 — 21.21 — — 10 14.5 9 — 4.5 51 — 21 —— 11 10 30 — — 30 — — — 30 Ta2O5 12 20 25 — — 30 — — — 25 Yb2O3 13 10 20— 40 30 — — — — 14 16 16 — 45 23 — — — — 15 20 20 — 30 30 — — — — 1635.7 — — 12.3 52 — — — — 17 20 — — 25 — — — — 55 P2O5 18 — — — — 72.8 —— 27.2 — 19 — 1 — — 71.8 — — 27.2 — 20 — 5 — — 67.8 — — 27.2 — 21 — 5 —— 67.8 — — 27.2 — 22 — 10 — — 52.8 — — 27.2 — 23 — 20 — — 52.8 — — 27.2— 24 — — — — — — — — — 25 — — — 34 66 — — — — 26 — — — 42 58 — — — — 2735.7 — — 12.3 52 — — — — 28 — 23 — 10 67.5 — — — — 29 — 10 — 14 76 — — —— 30 — 10 — 14 76 — — — — 31 — 3 — 16.4 80.6 — — — — 32 — 3 — 16.4 80.6— — — — 33 — 3 — 16.4 80.6 — — — — 34 — 5 — 29 66 — — — — 35 — 5 — 29 66— — — — 36 16 16 — 45 18 — — — 5 CeO2 37 16 16 — 45 23 — — — — 38 16 16— 45 23 — — — — 39 — — — — 60 40 — — — 40 30 — — — 40 30 — — — 41 — 0.75— — 71.6 — — 27.65 — 42 — — — — 73 — — 27 — 43 — — — — — — — — — 44 — 5— — 67.8 — — 27.2 —

The fillers used in Examples 5–44 were also characterized according toTest Procedures H–M. The results are summarized below in Table 8.

The designation “-” means not tested.

TABLE 8 Part. Sp. Fluores- BET Size gravity Exam. n_(D) XRD cence (m²/g)(μm) (g/cc) 5 — Am + very weak W/B 2.27 11.6 — unid. Ph. 6 1.528 Am N8.91 1.22 — 7 1.545 — N 1.41 8.28 — 8 1.549 — — — — — 9 — — B/W — — — 10— — — 0.51 18.2 — 11 1.514 — N 0.17 — — 12 — — — — — — 13 1.614 — B/W0.35 53.17 — 14 1.644 — Y 0.28 14.76 — 15 1.585 — N 2.2 2.45 — 16 1.528— — — — — 17 — — N — — — 18 1.540 — N 34.3 — 2.742 19 1.542 N 6.1 —2.708 20 — Am + ZrO2 — 5.8 — 2.690 (T, pc) 21 1.542 — N 2.36 21 — 221.538 — N 7.1 — 2.684 23 1.536 — Y 86 — 2.51  24 1.526 Am + ZrO2C — 20.5— — 25 1.522 — 1.55 — — 26 — Unid. Cry. Ph. — 10.36 — — 27 — — — 5.420.86 — 28 1.487 Am — 18.92 — 29 1.475 Am + very weak — 53.07 — — unid.Ph. 30 1.486 Am — 16.18 — — 31 1.500 Am — 13.99 — — 32 1.504 Am + very —49.01 — — weak, unid. Ph. 33 1.505 ∀-Cr + Unid. N 0.11 — — Cry. Ph. 34 —— — 50.84 — — 35 — — Y 2.85 — — 36 — — — 1.19 — — 37 1.644 — — 31.08 — —38 1.644 — — 2.4 — — 39 1.578 AM — 58.58 — — 40 1.532 AM — 0.49 — — 41 —— — <1 11.63 — 42 — — — <1 13.45 — 43 — — — — 5 nm — 44 — Am + ZrO2 —34.6 2.8 2.691 (tet/pc)

Each filler was used to prepare a composite as described in Example 1.The resin used in each example was Resin B1, with the exception ofExamples 11 (Resin B4), 12 (Resin B3), and 41–43 (Resin B4).

The hardness of each composite was evaluated according to Test ProcedureA at 30 minutes post-cure using the GYZJ-934-1 meter. The results arereported in Table 9. An Asterisk means that the Barcol value wasmeasured immediately after removing the visible light source.

TABLE 9 Example Barcol % Filler (w/w)  5 40 70  6 45 40  7 40 70  8* 4070  9* 30 40 10 55 70 11 58 70 12 48 70 13 55 70 14 55 70 15 — 70 16 5570  17* 38 70 18 55 40 19 55 50 20 55 70 21 50 70 22 40 60 23 40 40  24*30 57  25* 45 70  26* 45 70 27 45 70  28* 50 40  29* 50 40  30* 50 40 31* 50 40  32* 40 40  33* 10 70  34* 35 40  35* 45 70  36* 25 40  37*45 70  38* 30 40  39* 15 40  40* 15 40 41 60 70 42 60 70 43 — 70 44 5560

Examples 45–49

These examples describe the successful preparation of a number ofcationically polymerized compositions containing various radiopacifyingfiller blends. The various filler blends were prepared as follows:

Example 45

The filler sample consisted of a blend of 5 parts by weight of quartzfiller (filler (n)) and 2 parts of tin difluoride (Aldrich ChemicalCo.).

Example 46

The filler sample consisted of a blend of 5 parts by weight of quartzfiller (filler (n)) and 2 parts of zinc difluoride (Aldrich ChemicalCo.).

Example 47

The filler sample consisted of a blend of 5 parts by weight of quartzfiller (filler (n)) and 2 parts of bismuth oxide (Aldrich Chemical Co.).

Example 48

The filler sample consisted of a blend of 14.6 parts quartz filler(filler (n)) and 5.4 parts of colloidal zirconia filler.

Example 49

The filler sample consisted of a blend of 6 parts by weight of quartzfiller (filler (n)) and 10 parts of zinc difluoride (Aldrich ChemicalCo.).

Each filler blend was used to prepare a composite according to thegeneral procedure described above.

The hardness of each composite was evaluated according to Test ProcedureA at 30 minutes post-cure using the GYZJ-934-1 meter. The results arereported in Table 10.

TABLE 10 Filler % Example Barcol (w/w) Resin 45 52 70 B4 46 82 70 B4 4747 70 B4 48 60 70 B2 49 72 70 B4

Examples 50–52

These examples describe the preparation of radiopaque composites using anumber of different cationic polymerization initiators with UV light andheat. Each composite was prepared using Stock A1. Three differentphotoinitiators were used. The amount of photoinitiator in each case was2% (w/w). The filler in each case was filler (a). The filler loading ineach case was 50% (w/w). Initiation was accomplished using a combinationof ultraviolet radiation (supplied by a Fusion D lamp from FusionSystems) and heat (100^(∀) C. for 10 minutes). The total UV irradiationenergy was approximately 1500 mJ/cm².

The hardness of each composite was evaluated according to Test ProcedureA using the GYZJ-934-1 meter. The results are shown in Table 11. Theresults demonstrate that radiopaque composites can be successfullyprepared via cationic polymerization using a variety of cationicinitiators.

TABLE 11 EXAMPLE INITIATOR BARCOL 50 2% CD1012 50 51 2% CD1010 55 52 2%COM 55 CD1012 is diaryl hexafluoroantimonate (Sartomer). CD1010 istriaryl sulfonium hexafluoroantimonate (Sartomer). COM iscyclopentadienyl iron (II) xylene hexafluoroantimonate (3M).

CD1012 is diaryl hexafluoroantimonate (Sartomer).

CD1010 is triaryl sulfonium hexaflouroantimonate (Sartomer).

COM is cyclopentadienyl iron (II) xylene hexafluoroantimonate (3M).

Example 53

This example describes the preparation of composites using a hybridresin system featuring cationically active functional groups and freeradically active functional groups. The composites were prepared asdescribed in Example 1. The resin was an 80:20:30 blend of UVR-6105epoxy resin, polytetrahydrofuran 250 (M.W.=250 Da), and TMPTA(trifunctional acrylate). The resin contained 1.25% (w/w) CD1012iodonium salt and 0.5% (w/w) CPQ visible light sensitizer.

The hardness of each composite was evaluated according to Test ProcedureA using the GYZJ-934-1 meter. The results are shown in Table 12. Incontrast, when combined with only epoxy resin, both fillers resulted incomposites that failed to cure. The results demonstrate that radiopaquecomposites can be successfully prepared using hybrid resin systems.

TABLE 12 FILLER % FILLER BARCOL (w/w) (b) 65 70 (f) 80 70

Examples 54–60

These examples demonstrate that coated radiopacifying fillers featuringa core and a coating having a chemical composition different from thatof the core can be used to prepare composites from cationicallypolymerizable resins. The coated fillers were prepared as follows:

Example 54

This filler featured a quartz core with a zirconia coating. Quartzfiller (filler (n)) was dispersed in a colloidal zirconia sol (NyacolZRYS-4 ) under vigorous stirring such that the oxide composition yieldedwas approximately 10 wt % zirconia and 90 wt % quartz. The resultingslurry was spray dried and then fired at 1000° C. for 6 h. The resultingcoated filler particles had a B.E.T. surface area, measured according toTest Procedure H, of 0.75 m²/g.

Example 55

This filler featured a quartz core with a zirconia coating. The fillerwas prepared following the procedure of Example 54 except that thefiring step was omitted. The resulting coated filler particles had aB.E.T. surface area, measured according to Test Procedure H, of 4.04m²/g.

Example 56

This filler featured a quartz core with a zirconia coating. The fillerwas prepared following the procedure of Example 54 except that the oxidecomposition was approximately 50 wt % zirconia and 50 wt % quartz. Theresulting coated filler particles had a B.E.T. surface area, measuredaccording to Test Procedure H, of 0.75 m²/g.

Example 57

This filler featured a zirconia-silica core with a boria-silica coating.Zirconia-silica filler was made according to the procedure used toprepare filler (f), except that the steps after the first ball millingwere omitted. Under vigorous stirring, 800 parts by weight of thiszirconia-silica filler was slurried into 16000 parts deionized water and200 parts of a sol containing 532.9 parts of boric acid, 16765 partscolloidal silica sol (1042: Nalco Chemical Co.), and 3131 partsdeionized water. The coating thus applied had a nominal composition of 5wt % B₂O₃ and 95 wt % SiO₂. The resulting suspension was spray dried ina Niro spray dryer. The resulting powder was then fired at 850° C. for 6h. The resulting coated filler particles had a B.E.T. surface area,measured according to Test Procedure H, of 27.98 m²/g.

Example 58

This filler featured a zirconia-silica core with a boria coating. Thefiller was prepared following the procedure of Example 57, except thatthe firing temperature was 950° C. instead of 850° C. The resultingcoated filler particles had a B.E.T. surface area, measured according toTest Procedure H, of 2.63 m²/g.

Example 59

This filler featured an inorganic radiopaque zirconia-silica fillerdispersed in a cured methacrylate matrix. One syringe of 3M™ RestorativeZ100™ Incisal Paste was dispensed between two sheets of plastic film,squeezed to a thickness less than 1 mm, light cured in a KulzerDentacolor XS unit for 90 s, and milled in an alumina mill in a Spex8000 unit for 2 min. The B.E.T. surface area of the resulting coatedfiller particles was not measured.

Example 60

This filler featured an epoxy resin coating on a zirconia:silica sol gelfiller core. A blend of Epon 825 (80 parts), polytetrahydrofuran 250 (20parts), 1.25% (w/w) CD1012, and 0.5% (w/w) CPQ was magnetically coatedonto the surface of a zirconia:silica sol gel filler prepared accordingto the procedure used to prepare filler (f) except that all stepsfollowing the first ball milling were omitted. Magnetic coating wasperformed following the procedure described in WO97/07900. The coatedparticles were irradiated under a Sylvania UV lamp for 1 hour (600mJ/cm²) in order to cure the resin onto the surface of the particle.

Composites were prepared following the procedure described in Example 1.The hardness of each composite was evaluated according to Test ProcedureA using the GYZJ-934-1 meter. The results are reported in Table 13. Theasterisk means that hardness was evaluated using the GYZJ-935 meter.

TABLE 13 Filler % Example Barcol (w/w) Resin 54 55 70 B1 55 30 70 B1 5655 40 B1 57 48 50 B1 58 50 70 B3 59 43 60 B4 60  63* 30 B1

The results shown in Table 13 demonstrate that coated fillers featuring(a) a radiolucent core and a radiopacifying coating or (b) aradiopacifying core and a radiolucent coating can be used successfullyto prepare composites using cationically polymerizable resins.

Example 61

This example demonstrates that composites having good depth of cure canbe prepared using cationically polymerizable resins and radiopacifyingfillers.

Each filler was used to prepare a composite as described in Example 1.Each composite featured a filler loading of 70% (w/w) filler. Thepolymerizable composition used in each composite was Resin B4.

The depth of cure was evaluated for each composite according to TestProcedure F at depths ranging from 0 mm to 8 mm. The results, in theform of Barcol hardness values measured using the GYZJ-934-1 meter, arereported in Table 14. The designation “-” means not tested.

TABLE 14 Filler 0 mm 2 mm 3 mm 4 mm 5 mm 6 mm 7 mm 8 mm (a) 60 60 60 5540 40 40 40 Ex. 15 60 40 40 35 28 28 no cure no cure Ex. 42 60 60 60 5060 60 50 45 Ex. 21 — — — — — — — 10

The results shown in Table 14 demonstrate that depths of cure up to 8 mmcan be achieved using radiopacifying fillers.

Examples 62–64 And Comp. Ex. A

These examples demonstrate that useful dental composites can be preparedusing radiopacifying fillers and cationically polymerizable resins. Thefillers were prepared as follows.

Comparative Example A

Approximately 30 ml of a solution containing 1 part ethanol and 1 partdistilled water was weighed into a polyethylene beaker. Trifluoroaceticacid (Aldrich Chem. Co., Milwaukee, Wis.) was added to adjust the pH to4.5±0.1. 1.43 parts by weight of 3-glycidoxypropyltrimethoxysilane(G6720: United Chemical Technologies, Inc., Bristol, Pa.) was slowlyadded while stirring with a teflon coated magnetic stir bar.Approximately 30 mL of denatured ethanol was used to rinse the silaneaddition beaker, and this was then added to the hydrolyzing aqueoussilane solution. The solution was allowed to stir for about one hour atroom temperature to thoroughly hydrolyze the silane. 30 parts by weightof a filler blend of 98 parts of quartz filler and 2 parts of fumedsilica (Cab-O-Sil M5: Cabot Corp., Tuscola, Ill.) was slowly added tothe silane solution. The pH of the resulting dispersion was 4.94 at 36minutes after filler addition. The slurry was stirred overnight at roomtemperature before drying for 40 hours in a convection oven at 50° C.The dried cake was pulverized with a mortar and pestle and then shakenthrough a 74 micron nylon screen in a sealed container on a mechanicalshaker. The screened powder was then stored in a one pint glass jar witha foil lined paper seal to reduce moisture vapor transmission.

Example 69

A solution of 10 parts water and 10 parts ethanol was adjusted to a pHof 4.5±0.1 by addition of dilute trifluoroacetic acid (pH approximately0.5). 0.25 parts of 3-glycidoxypropyltrimethoxysilane (G6720: UnitedChemical Technologies, Bristol, Pa.) was added under vigorous stirring;the weighing beaker for the silane was rinsed with 20–30 ml of ethanol;then, the preparation was allowed to hydrolyze for 60 min. Next, 20parts of the filler sample prepared according to Example 21 was added tothe silane preparation under vigorous stirring; the slurry pH was 5.23.After allowing the slurry to stir overnight, it was poured into a glasstray and dried at 45–50° C. for 24 h; the resulting cake washand-crushed and passed through a 74 micrometer nylon screen.

Example 63

The filler was prepared by silane treating a portion of the fillersample prepared according to Example 27, 30 ml of a solution of 10 partswater and 10 parts ethanol was adjusted to a pH of 4.5±0.1 by additionof dilute trifluoroacetic acid (pH approximately 0.5). 0.72 parts of3-glycidoxypropyltrimethoxysilane (G6720: United Chemical Technologies,Bristol, Pa.) was added under vigorous stirring; the weighing beaker forthe silane was rinsed with 20–30 ml of ethanol; then, the preparationwas allowed to hydrolyze for 60 min. Next, 30 parts of the filler wasadded to the silane preparation under vigorous. After allowing theslurry to stir overnight, it was poured into a glass tray and dried at50° C. for 40 h; the resulting cake was hand-crushed and passed througha 74 micrometer nylon screen.

Example 64

The filler was prepared by silane treating a portion of the fillersample prepared according to Example 15. The silanation procedure wasthe same as for the filler sample of Example 63, except that 0.29 partsof 3-glycidoxypropyltrimethoxysilane were used instead of 0.72 parts.

Example 65

The filler prepared as described in Example 41 was ball milled with ¼inch alumina media and then annealed at 1000° C. for 6 hours. Theresulting filler was then silane treated as follows. Deionized water wasboiled until the pH reached 5.0–5.6, and then cooled to roomtemperature. 187 g of this water was mixed with 10 g of ethanol and 2.96g of glycidoxypropyl trimethoxy silane and the resulting mixture wasstirred for 30 minutes. 100 g of the filler was then added to thismixture to form a slurry which was stirred for 2 hours and then dried inan oven for 16 hours at 45° C.

Each filler was used to prepare a composite following the proceduredescribed in Example 1. The resin used in Example 65 was Resin B4. Theresin used in Examples A and 62–64 had the following composition:

20.54% (w/w) Heloxy 48 epoxy resin (Shell Chemical Co.);

61.61% (w/w) UVR 6105 epoxy resin;

16% (w/w) pTHF;

1.25% (w/w) CD1012;

0.5% (w/w) CPQ;

0.1 %(w/w) EDMAB.

The hardness (measured using the GYZJ-934-1 meter), compressivestrength, diametrile tensile strength, and visual opacity for eachcomposite were evaluated according to Test Procedures A, P, O, and Q,respectively, with the exception that the Barcol values were recorded 5minutes after removal of the radiation source. The results are shown inTable 15. The designation “-” means not tested.

TABLE 15 Comp. Filler Loading Strength Diam. Tensile Visual Example (w/w%) Barcol (MPa) (MPa) opacity A 80 54 272 75 0.53 62 76.7 50 219 56 — 6378.2 43 220 53 0.58 64 78.9 50 160 37 0.68 65 70 60 260 71.85 —

Example 66

This example describes the preparation of radiopaque composites in whichthe polymer matrix was derived from a vinyl ether. The composites wereprepared following the procedure described in Example 1. The resin usedin each case was Resin B6. The filler loading in each case was 50%(w/w).

The hardness of each composite was evaluated according to Test ProcedureA using the GYZJ-935 meter, with the exception that the Barcol valueswere recorded immediately following removal of the radiation source. Theresults are reported in Table 16.

TABLE 16 Filler Barcol None 0 Ex. 20 10 Ex. 22′ 30

“Ex. 22” means that the filler used in this composite was prepared asdescribed in Example 22 except that it was fired at 900° C. for 4 hours.

The results demonstrate that useful composite can be prepared usingvinyl ether resins as the matrix material. Both filled compositesexhibited higher Barcol values than the unfilled sample, demonstratingthat the filler did not inhibit the cationic polymerization mechanism toany appreciable extent.

Examples 67–79

These examples describe the preparation of a number of novel fillercompositions. The fillers were prepared as follows. Glass frits for eachfiller were prepared by weighing out appropriate precursors to yield theoxide compositions shown in Table 17. After blending, the batches wereheated to 1400–1650^(∀)C for a sufficient time to assure a homogeneousmelt, quenched in water, and dried. In all cases, a transparent glasswas obtained.

TABLE 17 Example A12O3 B2O3 La2O3 SiO2 ZnO Other 67 5 30 — 30 35 68 1025 — 25 40 69 15 25 10 35 15 70 15 20  5 40 20 71 15 25 — 30 30 72 20 2025 30 — 5Gd2O3 73 20 25 20 35 — 74 10 25 30 35 — 75 15 30 20 35 — 76 1515 30 20 — 2OTa2O5 77 15 35 — 30 — 2OTa2O5 78 20 20 — 30 — 3OYb2O3 79 1020  5 40 25

All values reported in Table 17 are given in weight %.

The properties of the fillers shown in Table 17 were evaluated accordingto Test Procedures J, L, and M. The results are reported in Table 18.The designation “-” means not tested.

TABLE 18 Example XRD Fluorescence n_(D) 67 Am + very weak N 1.585 unid.ph. 68 — — 1.599 69 — N 1.570 70 — N 1.560 71 — — — 72 — B/w — 73 — B/w1.558 74 — B/w 1.596 75 — N 1.541 76 — N 1.680 77 — N — 78 — N — 79 — N1.600

Other embodiments are within the following claims.

1. A melt-derived filler comprising 5–25% by weight aluminum oxide,10–35% by weight boron oxide, 15–50% by weight lanthanum oxide, and20–50% by weight silicon oxide.
 2. A melt-derived filler comprising10–30% by weight aluminum oxide, 10–40% by weight boron oxide, 20–50% byweight silicon oxide, and 15–40% by weight tantalum oxide.
 3. Amelt-derived filler comprising 5–30% by weight aluminum oxide, 5–40% byweight boron oxide, 0–15% by weight lanthanum oxide, 25–55% by weightsilicon oxide, and 10–40% by weight zinc oxide.
 4. A melt-derived fillercomprising 15–30% by weight aluminum oxide, 15–30% by weight boronoxide, 20–50% by weight silicon oxide, and 15–40% by weight ytterbiumoxide.